A ban on entry to foreign nationals who have travelled through mainland China has led to a major slump in visitor numbers.

She said the worst case scenario for her business was an estimated $3 million loss in revenue from exports to China, with the best case around half that.

"China is one of our larger markets," she said.

"We've found a huge drop-off in visitation, which is basically used as a showcase for our wines. It's been a bit disheartening coming on the back of the fires."

Earlier this week, Australia's biggest winery, Treasury Wine Estates, which owns the Penfold label, downgraded its profit guidance to the sharemarket due to the outbreak.

The company also said its staff in China had not been able to return to their offices because of controls put in place by Beijing.

The efforts to slow the spread of coronavirus has left opportunities to move into the lucrative Chinese market in limbo.

A number of trade events have been cancelled or postponed, including Chengdu’s annual China Food and Drinks Fair at the end of March. The event is considered one of the most influential places to showcase products.

Peter Dillon, chief winemaker at Handpicked Wines, said it was still too early to know just how big the impact on exports would be, however, there were already worrying signs in duty-free wine sales.

Those sales had dropped by about 80 per cent, he said.

"That side of the business is driven by the volume of traffic going through the airport and those numbers have crashed," he said.

"They're our biggest customers in terms of any market; it's very significant."

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Matt Fowles from Fowles Wine said there was an air of caution among winemakers about exports to China, however he was optimistic that the effect wouldn't be too bad.

He said the industry could even benefit from the "lipstick effect", a theory that consumers buy less expensive luxury goods in times of economic crisis.

"Wine's pretty good at riding out the tough times, because people drink when they're happy and drink when they're sad," he said.

James Hall, a consultant at Glenlofty Wines, said the outbreak had already resulted in a large order to China being delayed from January until the end of March.

"We can only wait and see what unfolds," he said. "At some stage it will finish, who knows when."