An oyster farmer is worried he may have no produce to show at the seafood festival in Brussels next week with ash clouds shutting down airspace over Europe.

Meteorologists from the UK have said volcanic activity in Iceland's Mt Eyjafjallajokull increased yesterday, forcing officials to extend flight restrictions yet again in an unprecedented air lockdown over much of Europe.

Biomarine director Jim Dollimore said the company was going to use the festival as a chance to break into the European market.

"We had sent some over in a container but they got damaged," Dollimore said.

He said he hoped the company would have some oysters to "back up its presence" at the show but if that is to happen, they will have to be on a plane by Friday.

Meanwhile a New Zealand firm has found a silver lining to the volcanic cloud shrouding Europe.

Marlborough's NZ King Salmon, is seeing a huge increase in orders from customers in Asia, whose usual suppliers in Europe are not able to fly their fish to export markets.

CEO Grant Rosewarne, said customers in Dubai, Bangkok, Singapore, Osaka and Tokyo, have all upped their orders substantially. Dubai's order is 100 times bigger than normal, while those from Bangkok have jumped tenfold.

Mr Rosewarne said they have doubled today's harvest and are putting on an extra shift to cope with an extra 10,000 fish.

Export New Zealand executive director Catherine Beard said many New Zealand exporters are relatively unaffected, as many products including dairy products, chilled and frozen meat, and kiwifruit, can be transported by ship.

She added that businesses exporting perishable goods to Europe are struggling, knowing it may be weeks before flights are back to normal.

Meat exporter Alliance is ruing the inconvenience for its customers abroad. Spokesman Gerry O'Connell said they have around 10 tonnes of chilled lamb, which cannot reach markets in Europe.

"We've got product halfway to the market in Singapore and LA and also product waiting here in New Zealand for departure."

Mr O'Connell said for the time being, meat in transit is being kept cold by Alliance's freight forwarders.