AFP/ Berlin

German airline Lufthansa said it cancelled 520 flights on Saturday, leaving 58,000 passengers grounded as cabin staff kept up a strike in a long-running battle over cost cuts.

While all domestic and European flights from Frankfurt and Duesseldorf were scrapped, inter-continental services were maintained, with the exception of one connection between Duesseldorf and Newark, New Jersey, a Lufthansa spokeswoman in Frankfurt said.

The airline had booked some 1,600 hotel rooms for Friday night, mainly in Frankfurt, for its grounded passengers, though around 50 people in transit were forced to spend the night in the airport because they did not have a German visa, the spokeswoman said.

Frankfurt and Duesseldorf airports -- Germany's busiest and third-busiest airports -- were hit Saturday by a walkout that began at 6:00 am (0500 GMT) and is scheduled to run until 11:00 pm (2200 GMT).

It is the second in a string of strike days planned from now through to November 13, though flights will resume on Sunday "because on that day, most flights are private", the UFO flight attendants' union said.

UFO on Thursday said industrial action was "unavoidable" after the management failed to come up with an improved offer in a long-running dispute over pay and early retirement provisions.

Lufthansa's subsidiaries Germanwings, Eurowings, Lufthansa CityLine, SWISS, Austrian Airlines, Air Dolomiti and Brussels Airlines are not affected by the industrial action.