Developers in Dubai have claimed a new record for the tallest building in the world, saying that the Burj Dubai skyscraper has now topped 688 metres (2,257 ft).

The slender, rocket-shaped tower is still under construction. Its final height remains a closely guarded secret, although it is expected to reach 800m.

Emaar Properties announced last summer that the skyscraper had surpassed Taiwan’s Taipei 101, which - at 508 metres (1,667 ft) - had been officially the world's tallest building since 2004.

In April this year, the Burj Dubai overtook the 628.8 metre KVLY-TV tower in North Dakota, a latticed tower supported by guy ropes which nonetheless remains the world's tallest completed structure.

At 553.3m, Canada's CN Tower in Toronto, Ontario, remains the world's tallest freestanding completed structure on land. The Petronius Platform stands 610 metres off the sea bed, leading the Guinness Book of Records 2007 to acclaim it as the largest freestanding structure in the world.

For the time being, Taipei 101 is still the world's tallest inhabited structure.

In a laconic statement issued today, the developer said that work on the exterior of Burj Dubai was now almost finished and construction would soon begin on the interior. So far the silvery steel-and-glass construction has soared more than 160 stories into the air. The company gave no further details.

The Burj Dubai tower has been four years in the building. After two postponements it is now due to be completed in September 2009.

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