Berlin's famous image as 'poor but sexy' may soon be replaced by a reputation for tardiness after a string of embarrassing setbacks for major city projects, including its troubled new airport.

For the fourth time in two years, the opening of Willy Brandt Airport to replace the German capital's two current hubs was put back last Friday after a grand 3 June opening was called off with just weeks to spare.

The airport is now scheduled to open its door on 27 October, 2013, well over a year late.

The debacle has prompted German newspapers to refer jokingly to the airport as "Wowi Fluchhafen", a play on the word for airport (Flughafen) and the word for curse (Fluch), as well as the name of Berlin's once-popular mayor.

Klaus Wowereit, head of the board of directors of the company in charge of the airport, has found himself flying through turbulence in recent months and has faced mockery, anger and criticism as the public face of the project.

A member of the centre-left Social Democrats, Wowereit, who coined the "poor but sexy" phrase about his city, has in the past figured on the shortlist of possible challengers to conservative Chancellor Angela Merkel.

"It's really embarrassing for the city as a whole," Ramona Pop, who heads the Green Party, the biggest opposition party in the city of Berlin's legislature, told AFP.

"Klaus Wowereit, as mayor and chairman of the board of directors wholly assumes the responsibility. The airport was his big main project and now, it's a disaster," she said.

She said she feared Berlin's image would be tarnished as a result.

"There are constantly headlines giving a negative image of Berlin, whether it's in the German press or the international media," she said.

"Capital of Failure" read a recent headline in German news magazine Focus which spoke of a city which "undoubtedly has charm... is even sexy for some" but where its "officials and politicians regularly fail".

Berlin's troubles have also featured in the international press.

The airport, also known as Berlin-Brandenburg International Airport, has turned from "an emblem of German know-how into a source of local embarrassment", the New York Times noted this week.

Its woes however have also led to a spotlight being shone on the capital's finances - it was €62.9-billion in debt in 2011 - and its other unfinished city projects.

The fat lady isn't singing...

The scheduled 2014 reopening of the city's oldest opera house, the Staatsoper, which closed in 2010 for refurbishment, has been postponed by a year due to the project running over budget.

And plans to rebuild the city's castle destroyed under the former communist East German regime are also in limbo.

For Berlin's city government, the delays and budget overruns are often down to "particular and totally unforeseen reasons", its spokesman Richard Meng has insisted, also suggesting some criticism is simply motivated by jealousy.

"It's always the reflex in Germany when there's something that is not running smoothly in Berlin," he said, adding people liked to knock Berlin which has enjoyed a good reputation.

And he pointed to the building of the Elbphilharmonie Hall in the northern port city of Hamburg which has been plagued by delays and a price explosion, as well as protests against a revamping of Stuttgart train station.

But Berlin's chamber of commerce and industry has sought to play down the impact of the delays.

"Berlin is still and always the city of creativity, a growing city, the capital of Europe's melting pot," its secretary general Christian Wiesenhuetter has said.

"And the airport arriving a bit later or a bit earlier will not change the reputation of the city much," he added.