The Burj Dubai, the world's tallest building, officially opens its doors Monday evening amid tight security, including plainclothes police. (Kamran Jebreili/Associate Press)

There's a lot of security and secrecy around the opening of the world's tallest free-standing structure in Dubai, due to be officially unveiled on Monday.

The Burj Dubai (Dubai Tower) is expected to measure more than 818 metres.

Bill Baker, the structural engineer from Chicago-based company Skidmore, Ownings & Merrill, says he wasn't sure just how high they would make the building, saying it was "a kind of exploration."

Toronto's CN Tower, at 553 metres, retains its Guinness World Record as the world's tallest tower. Guinness defines the Toronto landmark as a building in which less than 50 per cent of the construction is usable floor space.

By that definition, the Burj is definitely not a tower. Underway since 2004, it already boasts the most storeys and highest occupied space of any building in the world.

Emaar Properties, the Burj's developer, has kept quiet about the building's launch Monday evening.

Local reports say more than 1,000 security personnel will be on hand, including plainclothes police.

The opening comes at a poor time in Dubai's economy. Property prices have plummeted during Dubai's recent financial turmoil.

In late November, the investment arm of the Dubai government, Dubai World, defaulted on $59 billion US in debt and asked lenders for a reprieve on repayment until May. In mid-December, neighbouring Abu Dhabi threw it a $10 billion US lifeline.