Many of Europe's airports will run out of money unless passenger growth accelerates significantly, the European arm of Airports Council International (ACI) has warned.
It said that passenger traffic slumped 64.2pc in Europe during the first half of the year, and was down 96.4pc in the second quarter.
The organisation noted that following the "tentative coordination" of the lifting of travel restrictions in the EU by mid-June, the traffic recovery has been slower than expected.
That meant 208 million fewer passengers last month, bringing the total passenger decline to 969 million so far for the year.
It added that over the past two weeks, the pace of recovery has slowed down further as some countries re-imposed travel restrictions.
Olivier Jankovec, the director general of ACI Europe, said the recovery is "far too slow-paced and uncertain".
"Despite desperate efforts to trim down their costs, Europe's airports are burning cash at the height of summer," he said.
Mr Jankovec pointed out that airport revenues are weak because of a combination of low volumes and the provision of rebates and incentives to airlines in an effort to boost traffic.
"Considering the seasonality of demand, this does not bode well for the coming months," he said. "If the recovery does not accelerate significantly, many airports will simply run out of money."
The DAA, which operates Dublin and Cork airports, has previously said it has been losing about €1m a day since the middle of March as passenger traffic plunged at the facilities.
DAA chief executive Dalton Philips has predicted that it will take up to three years for passenger numbers to recover to 2019 levels.
However, some international forecasts point to a much longer recovery period.
Dublin Airport handled 32.9 million passengers last year, while Cork Airport saw 2.6 million travellers pass through its gates.
The DAA expects between 750 and 1,000 permanent jobs to go at the two airports because of the impact of the coronavirus.
ACI Europe said that non-EU airports in Europe had been less affected in the first half of the year, seeing a 59.8pc decline in passenger traffic compared to a 65.6pc fall in EU gateways.
It said that mostly reflected less stringent lockdowns in several non-EU countries, and domestic air services being less affected than international ones.