The federal government will spend $240 million to extend its international freight assistance scheme as borders remain shut.

Before the virus hit, about 90 per cent of exports were sent overseas in the bellies of passenger planes.

Trade Minister Simon Birmingham says the extension would provide ongoing certainty for exporters who rely on air freight.

"These freight flights have been vital to getting Australian produce out the door during these tough times and helping to keep local farmers and fishers in business," he said on Friday.

"Australian produce such as rock lobster, tuna and beef is in strong demand thanks to its reputation for quality, safety and reliability."

Since the program started earlier in the year, 1800 flights have exported 36,000 tonnes of produce worth an estimated $1 billion.

Rock lobster, salmon, tuna, beef, lamb, pork, poultry and dairy products are key exports.

Vegetables such as avocados, broccoli and strawberries are also sent overseas.

The majority of freight has gone to key markets in New Zealand, Singapore, Hong Kong, Malaysia, China, Taiwan, Vietnam, Thailand, Qatar, Kuwait and the UAE.

The extra money takes the total spent on the scheme to $350 million and secures about $3 billion in agricultural and aquacultural exports.

Australian Associated Press