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The Burj Khalifa dominates the skyline in Dubai, United Arab Emirates. The building is 828 metres tall and has more than 160 storeys, the most of any building in the world. ((Kamran Jebreili/Associated Press))

The world's tallest skyscraper formally opened Monday in Dubai.

 World's tallest buildings   Height (in metres) City
 Burj Khalifa  828  Dubai, U.A.E.
 CN Tower*  553  Toronto, Canada
 Taipei 101  509  Taipei, Taiwan
 Shanghai World Financial Center  492  Shanghai, China
 Petronas Twin Towers  452  Kuala Lumpur, Malaysia
 Willis Tower  442  Chicago, U.S.A.
 Jin Mao Building  421  Shanghai, China
 World Trade Center (Before collapse)  417  New York City, U.S.A.
 Two International Finance Centre  415  Hong Kong, China
 CITIC Plaza  391  Guangzhou, China
 Shun Hing Square  384  Shenzhen, China
Empire State Building 381 New York, U.S.A
*Guinness World Records once recognized the CN Tower as the world's tallest free-standing and tallest building. But, the Council of Tall Buildings and Urban Habitat disputes the designation of the comunications tower as a building.

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The Burj Khalifa is more than 160 storeys high, rising 828 metres into the sky.

The exact height of the new tower was kept under wraps by developer Emaar Properties until the tower was opened by Dubai's ruler.

The structure is about 250 metres higher than Toronto's CN Tower.

Thousands of residents and tourists gathered around the base of the massive building for its opening.

The building is apparently named in honour of Sheik Khalifa bin Zayed Al Nahyan, the ruler of Abu Dhabi and the president of the United Arab Emirates.

$9 million US per floor

The building cost about $1.5 billion US to build, or about $9 million US per floor.

Apartments in the building sold for $1,900 US per square foot at their peak, but prices have fallen by half in the wake of the financial woes that hit Dubai.

The city-state had to turn to Abu Dhabi for about $25 billion US in bailouts last year to cover amassed debts of state-linked firms.

While developer Emaar Properties is partly government-owned, it is not known if the firm got any bailout money.

"Crises come and go," said Emaar chairman Mohammad Alabbar in an interview prior to the building's formal opening.

"You have to move on. Because if you stop taking decisions, you stop growing."

Alabbar said the building is about 90 per cent sold.

With files from The Associated Press