A China foreign ministry spokesman confirmed on Monday that Chinese authorities have repeatedly found “biohazards” in imports of Australian timber.

China’s customs agency also said it had found contamination in barley shipments from Australian grain exporter Emerald Grain and had ceased imports from the company from Friday. The contamination was from bromus rigidus, a grasslike weed.

Major exporter Emerald Grain collects grain from around 12,000 grower families in New South Wales and Victoria and exports grain out of 17 grain terminals.

The bans on copper ore and copper concentrate, as well as sugar, are expected to be introduced this week, according to multiple trade sources in China.

In Shanghai over the weekend, Chinese customs seized a West Australian rock lobster shipment for laboratory testing. It is understood the shipment was a random sample and there are no details of when the results will be released. While testing is being undertaken, shipments of live lobsters have been stopped from entering China and remain quarantined in warehouses.

The Australian Seafood Trade Advisory Group has asked Australian exporters to stop sending live lobsters to China.

Australia’s trade minister, Simon Birmingham, said on Monday that the rock lobster shipments were being checked for “metal content levels” and the Australian government and industry groups were seeking further clarification from Beijing.

“We understand the concerns of industry in this regard, because of course this type of product is high value, but also has short time frames in terms of safely delivering the product from the Australian oceans to ultimately the marketplace in which they’re sold,” he said.

“And so, it’s crucial that timelines are kept to an absolute minimum when it comes to processing … it’s important today that people don’t jump to conclusions about what these delays mean, but enable our seafood industry working together with our diplomats and agricultural representatives to ascertain exactly what the facts are and whether we will be able to resume that trade with confidence [and] that customs processing happens in a timely way.”

China is also the main market for nearly all of Australia’s rock lobster exports, worth around A$750 million (US$527 million) last year.

China’s state-owned enterprises and private companies have also been informally instructed to stop buying seven categories of Australian products, namely barley, sugar, red wine, logs, coal, lobster, copper ore and concentrate from Friday, according to sources.

Goods that arrive at Chinese ports before Friday will be allowed to enter China, but those that arrive after will not be cleared by customs even if they are placed in a bonded warehouse.

Chinese importers which have shipments arriving after Friday have been told that they will have to bear the expense of uncleared goods and have been advised to cancel future orders to reduce their losses.

Chinese authorities verbally told Chinese steel mills and power stations to stop buying thermal and coking coal, leaving several Australian vessels stranded at Chinese ports and forward orders cancelled. Miner BHP Group confirmed it received deferment requests from Chinese coal customers.

No formal notice on the new bans was issued by the Chinese government, with many Chinese traders saying these “verbal bans” could complicate planning and ordering.

“This method could even make the conflict between China and Australia worse than the US-China trade war,” said one exporter, who did not want to be named due to the sensitivity of the issue.

While China is poised to host one of its biggest trade conferences this week, the China International Import Expo, its relationship with its biggest Asia-Pacific trading partner continues to suffer.