NEW YORK (AFP) - THE World Trade Center building complex in New York City, destroyed more than 13 years ago on Sept 11, 2001, has now officially risen from the ashes. A new similarly named skyscraper that has been built on the site of the tragedy reopened for business on Monday.

Signalling that America does not do its survival stories in halves, the revived building is now the tallest building in the United States, and the tallest structure in the Western Hemisphere.

One World Trade Cente on Monday welcomed its first tenants, publishing group Conde Nast, in a symbolic moment 13 years after the 9/11 attacks that brought down the original twin towers.

About 175 executives of the group that publishes magazines like The New Yorker and Vanity Fair filed through the doors of the building on Vesey Street, just steps from the memorial and museums, opened this year, erected at the site where the twin towers once stood. The skyscraper is at the centre of the site, which includes a memorial in the footprints of the old towers.

The iconic Manhattan landmark collapsed in fire and smoke on Sept 11, 2001 after being hit by hijacked airliners flown by Al-Qaeda militants. Nearly 3,000 people were killed in the attacks, which also targeted the Pentagon.

The new tower is the centerpiece of a five-tower complex. It stands at 104 storeys and 540m tall, or 1,776 feet, a height representing the year the United States declared its independence from Britain. It took eight years to build, at a cost of US$3.8 billion (S$4.9 billion).

"Some people are nervous, some people are just excited to move downtown and start a transformation for the company, to help revitalise lower Manhattan," said Mr John Duffy, director of policies and controls at Conde Nast.

Mr Duffy, who worked in the old World Trade Center in the 1980s, acknowledged that "some people are (going to) be nervous, feeling they could be potential targets again". But he said the authorities have worked hard to make a new building that is "probably indestructible".

Conde Nast messenger and mail clerk Dimitri Jones, 22, was quoted by Bloomberg as saying that he stayed up all night before coming for work on Monday, but not because of the 9/11 attacks.

"I love the way it looks," Bloomberg quoted him as saying. "I'm actually not nervous. I'm just ready to start. It was a tragedy, but I'm ready to move forward."

Describing the building's opening as "truly a miracle", Mr Steven Plate, director of World Trade Center construction for the Port Authority, was quoted by Bloomberg as saying: "We're very proud to turn this over as a gift to New York City and the people lost on that fateful day."

Conde Nast is expected to have a total of 3,400 employees in January spread across floors 20 to 44 of the building.

One World Trade Center, designed by architect David Childs, has become a Big Apple landmark of its own, with simple lines, a needle-like spire and mirrored windows that shimmer brightly in the sunlight.

Operated by the Durst Organisation, the building is owned by the Port Authority of New York and New Jersey, a governmental agency.

Its other tenants include the China Center New York, Legends Hospital Group and the General Services Administration, which supports the basic functions of federal agencies.

Durst Organisation spokesman Jordan Barowitz told Agence France-Presse that 60 per cent of the office space is already rented.

Mr Douglas Durst, whose real estate company manages and leases the 3 million sq ft tower on behalf of the Port Authority of New York and New Jersey, said he expects the pace of leasing to pick up now that the building is open. "When you take people into a construction site, it's very different from taking them into a finished, open building with a working lobby," Mr Durst said, according to Bloomberg. "I've been in the business for 40 years, and I've seen this happen before."

For Vanity Fair publisher Chris Mitchell, the site's reopening marked "a great day for New York and a great day for Conde Nast, an amazing experience for the company".

He spoke to reporters at a corner of the tower, with the police keeping a close watch on the area.

The public will be able to access an observation deck on floors 100 to 102, which is to open in the spring.

The new WTC complex includes five towers, a memorial and museum that opened in May, a centre for the performing arts and about 55,000 sq ft of retail space that connect to an extensive transportation network.

Calling itself a "shining beacon for New York's downtown", the One World Trade Center has a sustainable design at its core that integrates renewable energy, interior daylighting, the reuse of rainwater and recycled construction materials.

As for safety, the building features dense fireproofing, biochemical filters, extra-wide pressurised stairs, multiple backup emergency lighting, and concrete protection for all sprinklers.

"Exits are designed to ensure easy evacuation, and all safety systems are encased in the core wall, with the enhanced elevators," according to the site's property managers.

"The New York City skyline is whole again," the BBC quoted a statement by Mr Patrick Foye, executive director of the Port Authority.

He added that the building was "the most secure office building in America", according to the BBC.

The first new building erected at the site of the attacks was Four World Trade Center, designed by Japanese architect Fumihiko Maki. It opened in November 2013.

Footage released of the view from the steel spire at the top of the new skyscraper showed the final section of the 125m spire being installed on top of the building last week.