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Korean Air has warned the coronavirus outbreak could threaten its survival in a memo sent to employees.

South Korea has been hit hard from travel restrictions aimed at curbing the spread of the virus.

Its national carrier has cut more than 80% of its international capacity while encouraging employees to take voluntary leave.

In the memo, Woo Kee-hong, Korean Air's president said the airline couldn't predict how long the crisis would last.

"But if the situation continues for a longer period, we may reach the threshold where we cannot guarantee the company's survival," he said in the memo, which was seen by Reuters.

A spokesman for Korean Air told the BBC the purpose of the internal memo was "to encourage employees and ask for understanding to overcome the crisis together".

"We have gone through numerous difficulties for the past 51 years, and I'm confident that we will overcome this crisis together," he said.

'Temporary layoffs'

The airline industry has been struggling with a sharp downturn in passengers numbers with travel restrictions in place and an unwillingness to fly during the virus outbreak.

Norwegian Air has said it will cut about 3,000 flights in the next three months, about 15% of its capacity.

The company will also temporarily lay off "a significant share of its workforce", it said in a statement.

"We have initiated formal consultations with our unions regarding temporary layoffs for flying crew members as well as employees on the ground and in the offices," said chief executive Jacob Schram.

The International Air Transport Association, a trade body, estimates the virus could reduce passenger revenue globally this year by between $63bn and $113bn.

Carriers across the world have been introducing hiring freezes and asking staff to take unpaid leave along with grounding planes.

On Tuesday, Australia's Qantas said it was cutting more flights, with routes to Asia and the US hit the hardest.

The company said it would reduce international flights by nearly 25% as it sees demand fall from passengers worried about the coronavirus.

Qantas and its budget airline Jetstar will reduce operations for the next six months.

It will ground eight of its 10 double-decker Airbus A380s and replace them with smaller planes while reducing the frequency of flights.

"We expect lower demand to continue for the next several months, so rather than taking a piecemeal approach we're cutting capacity out to mid-September," Qantas chief executive Alan Joyce said.

Mr Joyce said he will forgo some of his A$24m (£12m) salary while other Qantas executives will take a 30% pay cut during the downturn.

UK-based Flybe was the first casualty of the coronavirus, going into administration last week. Analysts warn others could follow.