World Trade Centre site back in business after September 11 with tallest building in the US

One World Trade Centre takes the place of the Twin Towers 13 years after 9/11

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The World Trade Centre opened its doors for business today 13 years after the 9/11 tragedy, with America's newest and tallest skyscraper that has made the "New York City skyline whole again".

The $3.9 billion (£2.4bn) building, named One World Trade Centre, takes the place of the Twin Towers which burned and then collapsed after two planes were flown into them on 11 September 2001, killing 2,700 people.

Publishing company Conde Nast is today set to move 170 of 3,400 employees into five floors of the building, which has been called by executive director of the Port Authority of New York and New Jersey Patrick Foye as "the most secure office building in America".

He said the 1776ft structure completes the Big Apple's skyline and "sets new standards of design, construction, prestige and sustainability... the opening of this iconic building is a major milestone in the transformation of Lower Manhattan into a thriving 24/7 neighborhood."

Around 3,000 of Conde Nast's staff will move into the skyscraper early next year, confirmed the firm's vice president and spokesperson Patricia Rockenwagner.

An observation deck is planned to open to the public on the glass building that took eight years to build and has been strengthened by steel-reinforced concrete.

The building is 60-percent leased, with another 80,000 sq ft set aside for advertising firm Kids Creative, stadium operator Legends Hospitality, the investment advisers BMB Group, and Servcorp, a provider of executive offices.

Ground Zero, the site of the collapsed buildings where bodies and debris lay, has been transformed into the National September 11 Memorial & Museum, which pays tribute to those who died on that morning.