Estimated global airline losses from the coronavirus pandemic have climbed to $314 billion, 25% more than previously forecast, owing to the severity of the economic downturn and a slower than previously expected reopening of international routes.

The latest forecast from the International Air Transport Association (IATA) is up from the $252 billion figure given on March 24 and represents a 55% drop in 2020 passenger revenue compared with last year.

Traffic measured in revenue passenger kilometres is forecast to be 48% down this year, compared with the previously forecast 38% decline, industry body IATA said at a weekly online news conference on Tuesday.

"The recovery should be slower and the crisis deeper than we expected even one month ago," Director General Alexandre de Juniac told Reuters TV in an online interview.

The pandemic has brought air travel to a virtual standstill, with many airline fleets grounded and no visibility on when travel restrictions will be eased.

IATA has urged governments to provide airlines with liquidity urgently to help them to survive the crisis, warning that many will go bust within weeks unless they receive help.

The trade body, which represents airlines such as Lufthansa and British Airways owner IAG, said it expects domestic markets to be the first to reopen, as has happened in China, with international routes following gradually.

A phased return of international flights would still be problematic for airline finances because most carriers obtain the bulk of their revenue from international routes, IATA said.

IATA urged nations to co-operate on the lifting of restrictions and said it would organise a series of regional meetings to weigh a "restart plan" for the industry.

"These measures that have been implemented unilaterally by each state have to be lifted jointly otherwise it will not work," de Juniac said.

"You cannot say you authorise your citizens to go abroad without having on the other side a state saying 'I am ready to welcome them'."

IATA was embarking on a three-stage plan to boost passenger confidence in flying, restore the confidence of governments and gain approvals from health authorities, he said.

IATA has started a survey of passengers in 11 countries to understand the depth of concerns about air travel.

De Juniac told Reuters TV restoring demand would depend in part on measures such as controls and testing, and availability of specialist equipment.

Once governments decide it is appropriate to lift travel restrictions, flying will be safe "provided that these measures are properly designed and properly implemented," he added.