Australia's biggest airline Qantas said it would halt all international flights and suspend 20,000 staff in response to the coronavirus pandemic Wednesday, days after the island nation's other main carrier Virgin shut its overseas routes.

Qantas said all of its international flights would be suspended by late March for at least two months after the government told citizens Wednesday to forego all overseas travel in a bid to halt the spread of novel coronavirus.

"The efforts to contain the spread of coronavirus have led to a huge drop in travel demand, the likes of which we have never seen before," Qantas chief executive Alan Joyce said, adding that the airline would suspend 20,000 of its 30,000 staff during the shutdown.

The move also affected Qantas' budget offshoot, Jetstar. A number of foreign airlines also service Australian routes.

Qantas announced earlier this week a 90 percent cut in overseas flights while Virgin Australia grounded its entire international fleet.

Qantas is maintaining 60 percent of its domestic flights and Virgin Australia 50 percent.

Airlines worldwide face an unprecedented existential threat as the coronavirus shuts down global travel, leaving governments with controversial and costly decisions about which carriers to bail out.

The Transport Workers' Union said Qantas was making staff foot the bill for the crisis.

"This plan is designed to wipe the slate clean on all worker entitlements, including long-service leave and accrued benefits," union secretary Michael Kaine said in a statement. 

Qantas shares were down almost 12 percent on Thursday.

- Imported virus cases -

Australia has reported more than 600 confirmed cases of coronavirus, with infections increasing daily. There have been six deaths.

Officials say a large number of new cases involve people arriving from overseas or those who have been in contact with them.

On Wednesday, Prime Minister Scott Morrison announced an unprecedented decision to advise all Australians to forego foreign travel.

He has also ordered a halt to all cruise ship activity into and out of the country, banned outdoor gatherings of more than 500 people and indoor groups of more than 100. But he stopped short of ordering the kind of lockdown seen in some pandemic hotspots or closing the nation's schools.

Meanwhile, the island state of Tasmania announced Thursday than any non-essential travellers arriving in the island from Saturday would have to self-quarantine for 14 days.

The move, the first by any Australian state to restrict domestic travel, excludes health workers and essential personnel dealing with trade.

Tasmania, off Australia's southern coast, has a population of around 500,000 and has reported just 10 cases of coronavirus.