Tens of thousands of passengers were stranded in Berlin on Friday as a strike by ground staff led to the cancellation of nearly 700 flights operated by airlines including Air Berlin, Ryanair and Lufthansa.

Berlin Airport, which operates Tegel and Schoenefeld airports, said almost all flights from the German capital had been grounded, with 466 flights cancelled at Tegel and 204 at Schoenefeld as of 0900 GMT.

The industrial action comes as many trade visitors try to make their way home from the world's biggest tourism trade fair, the ITB, which ends in Berlin on March 12.

Some delegates left the trade fair early to avoid the strike while others told Reuters they faced long train journeys or detours to other German airports such as Hamburg or Dresden.

Air Berlin said it had cancelled 202 flights, with only long-haul routes and flights to and from Duesseldorf still operating. It offered passengers vouchers for train tickets to their German destinations or flights from Hanover.

Irish budget carrier Ryanair cancelled 77 flights to or from Berlin and said it was offering customers a full refund, free transfer onto the next available flight or a free transfer onto an alternative flight route.

German flagship Lufthansa said it had had to cancel 68 flights between Berlin, Frankfurt and Munich, affecting about 10,000 passengers, who could rebook or cancel for free.

"Everything should return to normal on Saturday," a Lufthansa spokesman said.