German politicians warned Friday of possible further delays to Berlin's troubled new airport project, already five years behind schedule, after an engineering company involved filed for bankruptcy.

Project leaders said they were reviewing the impact of the news that the German division of Dutch group Royal Imtech, that is handling major electrical, ventilation and plumbing work at the site, had filed for bankruptcy Thursday.

The German capital's new international air hub has become a multi-billion-euro planning disaster and a running joke for many Berliners, tarnishing Germany's reputation for engineering prowess, efficiency and punctuality.

Originally set to open in 2012, the BER airport is meant to replace two smaller airports, Tegel and Schoenefeld, vestiges of the city's Cold War division that are now bursting at the seams.

After several delays and budget blow-outs due to serious technical flaws -- especially in the fire safety and smoke extraction system -- officials now hope to open BER in late 2017. But even that date seemed in serious doubt after the latest setback.

"I believe the opening date is in great danger," said the chairman of Berlin's committee of inquiry into the airport fiasco, Martin Delius of the Internet freedom Pirate party, whose concerns were echoed by a far-left Linke party member on the panel.

Delius told Berlin public radio that project leaders should have searched for alternatives to Imtech long ago, adding that building a ventilation system is "not rocket science".

Members of the airport supervisory board voiced "concern" about the Imtech news, said national news agency DPA.

Amid BER's spiralling woes, the giant glass and steel building on the capital's southeastern outskirts has become a growing money pit.

A "ghost train" to the city centre now runs to it empty once a day to prevent the rails from rusting and tunnel walls from gathering mould.

Further troubles may be brewing for the project, which is financed by the federal government, the city-state of Berlin and the Brandenburg region, reported Berlin's Tagesspiegel daily.

Anti-BER resident groups worried about aircraft noise have filed a complaint with the European Commission, it reported, arguing that the "exorbitant and apparently limitless" public funding for the airport breaches competition rules.