German authorities Monday ordered an immediate halt to construction work on Berlin's troubled and long-delayed new airport after finding possible structural flaws in the terminal roof.

The latest bad news to hit the BER airport project risks further delaying its opening -- initially planned for 2012 but repeatedly pushed back, with the date now set for late 2017.

The latest problem discovered is that ventilators built into the roof may be too heavy, meaning the soaring structure "exceeds the approved weight limit by a significant amount".

The building authority for the Dahme-Spreewald locality said it had told the construction firm Monday to "immediately stop building works for the area underneath the entire terminal roof of the BER airport" until security checks could be carried out by engineers.

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.

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 two years' time.

But even that date has looked optimistic after recent setbacks, including the bankruptcy of the German division of Dutch group Royal Imtech, which is handling major electrical, ventilation and plumbing work at the site.