Shipments of Australian products could be turned back at the Chinese border, industry insiders fear, as confusion reigns over Beijing's clamp down on online sales.
On the eve of Prime Minister Malcolm Turnbull's arrival in China, Australia's biggest vitamin and dairy companies are desperately seeking clarification over regulatory changes that have smashed their share prices.
More than $800 million has been wiped off the combined market value of Blackmores, Bellamy's and A2 Milk in the past three days, after Chinese authorities imposed an 11.9 per cent tax on products bought from foreign websites and created a "positive list" of products allowed to enter the country via free-trade zones. 
Under the changes, goods deemed healthcare products must have approval from Beijing before they can be sold in China through the country's cross-border e-commerce channels.
Industry insiders say products that do not have approval - which can cost $200,000 per item and take two to three years - will be stopped at the border and potentially be sent back to Australia.
"They need very serious import permissions. If they don't have import permission they can't get into the bonded area," said Richard Zhang, founder and chief executive of Rex Group, which specialises in importing Australian goods through Chinese cross-border warehouses. "That's a serious matter."
The rule changes only affect the cross-border warehouses that have exploded in popularity due to both logistical and tax efficiency. More expensive methods, including direct shipping, remain viable to the extent that Chinese consumers are willing to pay higher prices.
The policy chaos - and the hammering of share prices of Australian companies such as Blackmores - was a hot talking point among trade mission delegates visiting the Hangzhou Xiasha cross-border bonded warehouse, a massive facility where goods arrive on a 12-metre container and leave in individually packaged parcels to Chinese homes.
Goods such as raw and fresh products, as well as liquid milk, are not included on the exhaustive "positive list". Over the weekend, flagship online stores like Alibaba's Tmall had taken Australian long-life milk brands like Murray Goulburn's Devondale off their virtual shelves.
Murray Goulburn managing director Gary Helou said he understood why Beijing had tightened the regulation of imported foreign goods, given the popularity of cross-border e-commerce websites.
"There has been rampant growth across the cross-border bonded stores and you'd expect the regulators to put some checks and balances into it, so that piece is not a surprise," said Mr Helou.
"What we are seeking, though, is clarity on exactly what that list has on it, and should have on it."
  Trade mission  
Mr Helou - who is in China with 1000 other business leaders who are joining Mr Turnbull on what has been dubbed as Australia's largest ever trade mission to the country - said he didn't expect the changes to "materially" hit Murray Goulburn's overall sales into China.
He said the co-operative had a wide distribution network across the country and had strong partnerships with conventional importers.
Blackmores chief executive Christine Holgate said shipments of the company's products were still being processed in China and she did not expect that to change. She said Blackmores had approval for all its main products it sold in China and the cross-border e-commerce platform represented only 3 per cent of the company's overall sales.
"People are getting confused over the listing environment for the retail environment and the listing environment for the free-trade [cross-border e-commerce] environment," Ms Holgate said.
"There are many routes to the Chinese market. But the [cross-border e-commerce route] is an important route and a route that is growing and I don't want to undervalue it, and it is pleasing that the Chinese government is giving it such focus, because it's indicative that they want this trade to continue."
Fairfax Media can reveal that China's four biggest online retailers - Alibaba, JD.com, VIP.com and Yihaodian - are having high-level meetings with Chinese officials to clarify the law changes for their Australian, US and European retail partners.
A senior industry source told Fairfax Media on Tuesday that there was "a need for clarification" from Chinese authorities, which was responsible for Tuesday's volatile share prices.
"We know the big four online retail platforms are in high-level talks with the Chinese government," he said.
"These four retailers represent the majority of online sales for Australian producers in China. We should have some clarification in the next 48 hours."
Meanwhile Bellamy's chief executive Laura McBain expected trade in China to continue as normal, given infant formula was on the "positive list".
"That's the main game for us," Ms McBain said.
Morgans analyst Belinda Moore said: "Concerns around a China slowdown and regulatory changes are clearly impacting the share prices of the agrifood stocks which sell into China, particularly those that sell through cross-border e-commerce channels."
"However, the ??? outlook commentary from the respective companies demonstrated that there is no slowdown for quality and, importantly, safe Australian food in China.
"It's going to be volatile and there will be more changes. But the fact is China has signed an FTA [free trade agreement with Australia] and they have done that because they want more and more of our produce.
"So there is a big opportunity for Australian manufacturers to continue to win market share in this large market."