Air France-KLM said it had narrowed its loss in the second quarter and saw the "first signs of recovery" in the aviation sector as countries ease coronavirus restrictions and vaccination campaigns continue apace.

The French-Dutch airline said in a statement that it booked a bottom-line net loss of €1.5 billion in the period from April to June, narrower than the €2.6 billion for the same period a year before.

"Thanks to the easing of travel restrictions in several key regions, the second quarter of 2021 saw the first signs of the long-awaited recovery," said chief executive Benjamin Smith.

"Reciprocity of borders reopening and the acceleration of the vaccination roll-out worldwide, especially in the context of the rise of the Delta variant, will play a key role in maintaining this momentum."

The renewed second-quarter loss brings the airline's cumulative loss since the start of the pandemic to more than €10 billion.

Second-quarter revenues more than doubled to €2.75 billion euros from €1.2 billion euros a year earlier as passenger numbers soared to 5.85 million from 1.13 million.

"Since June, first signs of recovery are visible in the booking trend thanks to waived or eased travel restrictions in Europe due to the rise of vaccination rate across all countries," Air France-KLM said.

"The reopening of the North Atlantic for American citizens to visit Europe also resulted in an improved booking trend."