The addition of copper ore and sugar to a growing list of commodities targeted by Chinese authorities alarmed the agricultural and mining sectors, which were on Tuesday scrambling to verify the authenticity of the notice.

Shares in major exporters to China fell on reports of the possible ban. Copper miner Sandfire Resources fell more than 8 per cent and Treasury Wine Estates, which holds its annual meeting on Thursday, lost more than 3 per cent.

The Morrison government is yet to confirm the existence of the sweeping edict against Australian goods but was working closely with the named industries and continued to seek clarification from Chinese officials.

"The numerous reports of difficulties that different Australian exports are facing on entry into China are of concern," Trade Minister Simon Birmingham said.

Some traders in China questioned the legitimacy of the directive, which also listed wine, coal, cotton, lobster, timber and barley as targets of a ban to be enforced from Friday. Those goods are either the subject of anti-dumping probes by China or have already had partial restrictions put in place.

However, Australian exporters said it was too widespread to ignore as some Chinese customers were already cancelling shipments based on the advice. "It seems very odd to me but for all our exporters, their importers are telling them things will happen this week and they are cancelling shipments," Tony Battaglene, chief executive of industry group Australian Grape and Wine, said.

The move came as China banned timber from Queensland and blocked trade from an Australian barley exporter after customs claimed pests found in the imports threatened the country's ecological security. There were also unconfirmed reports on Tuesday that China would target Australian wheat.

Grain Producers Australia chairman Andrew Weideman said recent strength in the wheat trade had offered hope of rebuilding relations between the industry and China.

“If the reports are true, it is of great concern to us. There is no question of that,” Mr Weideman said, noting the industry had previously hoped to rebuild relations off the back of the strength in recent trading.

Sources said China's Commerce Ministry had verbally told food and wine importers at meetings in three cities on Friday not to initiate further orders for the six Australian commodities ahead of a possible ban. But traders and distributors interviewed on Tuesday questioned the authenticity of the directive.

Two traders said they could not verify the list, which appeared to be from a city-level authority because it contained the word "bureau" and not "ministry", which would have indicated it was a China-wide directive.

Regardless, China was sending a clear message to Australian exporters that had spooked local food and wine distributors, who would start to cut back purchases anyway because they feared shipments would be either banned or subject to extensive inspections.

"The message is clear. China will be tough on Australian goods but no one knows how strictly this will be implemented," one distributor in the grains industry, who did not want to be named, told The Australian Financial Review.

Mr Battaglene said the grape and wine industry body was bracing for the worst for the $1.2 billion market.

"Importers are actively cancelling shipments," he said. "What we don't know is whether it is importers trying to toe the line or directions from above. We are all pretty sure that come Friday the market will be closed."

The latest move comes ahead of the US election and follows restrictions on Australian barley, beef, coal and cotton. China has warned its students and tourists to avoid Australia and has begun an anti-dumping investigation into wine. Under that probe, China could technically impose tariffs at any time.

Madeleine King, shadow minister for trade, called on the government to appoint a trade minister and rethink the way it dealt with China. "The government should be more measured in the way it communicates about China," she said.

China confirmed on Monday night it had detected cases of pests in timber imported from Australia since January but refused to directly address suggestions on a second wave of possible restrictions on other goods.

China's Foreign Ministry said its inspection and quarantine measures on imported seafood were in line with its laws but several times emphasised "mutual trust" as the foundation for a trading relationship between the two countries.

"We hope Australia can do more things conducive to mutual trust, bilateral co-operation and the spirit of China-Australia comprehensive strategic partnership, and bring the bilateral relations back to the right track as early as possible," a Foreign Ministry spokesman said, when asked if the latest reported restrictions were designed to punish Australia politically.

Emerald Grain, an Australian-based trading company owned by Japan's Sumitomo, said on Tuesday it was the victim of a trumped-up and politically motivated ban after big Chinese malt-makers continued to buy Australian barley in defiance of Beijing's efforts to shut the trade.

Sandfire Resources said it was aware of reports that China may be considering a ban on imports of copper ore and concentrate but was not aware of any reasons for the reported restrictions.

Shares in the miner fell 6.5 per cent at lunchtime on Tuesday. The company said it was confident of increasing sales to non-Chinese markets if necessary.

China's Foreign Ministry said it had asked Australia to investigate the presence of live pests in timber, such as longicorn and buprestid beetles, which had been found in imports since January.

"We hope that the Australian side will take effective measures to strengthen export quarantine and ensure the exported timber meet China's quarantine requirements," the spokesman said.

China did not deny allegations it was conducting a campaign of economic coercion on Australia following the Morrison government's call for an inquiry into the origins of coronavirus.

Customs officials on Sunday warned they would step up inspections on timber, barley and lobster as rumours swirled of restrictions on other key agricultural commodities such as wine, sugar and copper.

About 21 tonnes of live lobster worth $2 million has been held up at Shanghai airport since Friday after Chinese customs officials changed inspection procedures. The exports were sent to China on Australian taxpayer-subsidised flights.

Chinese nationals are buying Australian vineyards and wineries at unprecedented levels, with up to 10 per cent of South Australia's iconic Barossa Valley now in Chinese hands.

"If I look at the last seven transactions I have personally done … six of them have been to Chinese parties," said Stephen Strachan, director of Langley and Co, a company dealing in wine industry acquisitions.

"Most probably 50 per cent of the calls that we get into our office are from Chinese parties or from parties representing Chinese interests."

The former chief executive officer of the Winemakers' Federation of Australia said the investments had become "more sophisticated".

"Probably five years ago when this started all roads led to the Barossa, and the typical conversation would be 'I want to buy Penfolds'," he said.

"A lot of the original parties were looking for trophy assets and the Barossa was number one, but progressively that has changed and other regions like McLaren Vale, the Yarra Valley, there's been strong interest in Margaret River, and a little bit in Coonawarra, so Australia's other regions are starting to have some significant success in China."

China’s President Xi Jinping has told thousands of foreign exporters that Beijing does not want to hurt other economies as Chinese state media reports a $6 billion ban on seven key Australian products is imminent.

Australian businesses across seafood, wine, barley, sugar, copper, coal and timber industries are bracing for a sudden halt to their exports to China today as up to 200 gather in Shanghai for one of the country’s largest import conferences.

Xi told the China International Import Expo on Wednesday night that countries must work together to find a way out of the coronavirus recession.

‘‘It is ill advised to pursue unilateral dominance, or choose to hurt others’ interests, which diminishes one’s own interests,’’ he said.

Trade Minister Simon Birmingham escalated Australia’s response to Chinese authorities yesterday, addressing Xi’s comments directly as trade negotiators prepare for the possibility that key exports could be locked out of China within 24 hours.

Some Australian wine exporters have stopped sending product to China in anticipation of being blocked at Chinese ports, while lobster fishermen have stopped fishing in Australian waters after tonnes of live lobster were destroyed on the tarmac at Shanghai airport this week. Up to 90 per cent of Australia’s lobster goes to China. Queensland timber logs have also been blocked over pest control concerns.

‘‘Continued uncertain and inconsistent messages from China are heightening risks and undermine the statements made by President Xi at this year’s China International Import Expo,’’ Senator Birmingham said.

‘‘If China is to be true to the statements of its government then it should provide confidence that normal customs and related processes will apply to imports of goods such as seafood and wine.’’

The trade dispute escalated this year following Australia’s push in April for an inquiry into the origins of the coronavirus. The Australian government has also raised concerns about the future of Hong Kong, Xinjiang and China’s ambitions in the South China Sea.

The Chinese Foreign Ministry has denied it is ratcheting up economic pressure to win diplomatic concessions. On Wednesday, a day after a verbal notice relayed by customs agents was delivered to traders telling them to stop importing Australian products, it said any restrictions on imports were a matter for individual companies.

Chinese state media outlet The Global Times yesterday said China had ‘‘halted seven categories of Australian goods from the market’’. The report came as Graham Fletcher, Australia’s ambassador to Beijing, prepared to attend the trade expo in Shanghai, where dozens of representatives from Australian companies were due to gather under ‘‘the Oz-Town Australian Pavilion’’.

The Australian industries targeted by Chinese authorities have produce that can be sourced from elsewhere and are not seen as critical to China’s economic recovery.

Australia’s largest exports, iron ore and coal, account for more than $120 billion of Australia’s annual exports to China.

China is heavily reliant on Australia to supply the huge quantity of iron ore it needs to produce steel for construction and infrastructure projects.

However, coal imports are more vulnerable to restrictions as China has a significant domestic coal mining sector, which Beijing has been seeking to strengthen.

Xi told the expo China had set out to foster ‘‘a new development paradigm with domestic circulation as the mainstay’’ and domestic and international trade reinforcing each other.