Prince Harry, who is known in New York as the Party Prince, was in more sombre mood for his first official engagement overseas today.

Less than two hours after landing in New York, the 24-year-old Prince was whisked to the World Trade Centre (WTC) site to lay a wreath to commemorate almost 3,000 people who died in terrorist attacks there on February 26, 1993 and September 11, 2001.

Harry arrived at the site in downtown Manhattan in glorious sunshine, dressed in a dark blue suit with maroon striped tie.

Bypassing the cheering crowds, he walked briskly through a tunnel, emerging into the sunlight where the towers once stood. He glanced upwards, seemingly taking in the enormity of the structures felled in the attack, and said simply: “Wow”.

For the first engagement of his trip — paid for privately by the Queen — Harry inspected the building site where seven buildings, including the collapsed twin towers, had stood, and met local fire fighters.

Monica Iken lost her husband Michael Patrick Iken, who was at work on the 84th floor of the second tower when it collapsed, only 11 months after they married and a day after Michael's 38th birthday. His body was never recovered.

Mrs Iken said that it meant "so, so much" that Prince Harry's time in the army gave him a personal connection to the WTC. “He knows this is where the whole War on Terror started," she said.

After the WTC, it was on to the British Garden in Manhattan’s Hanover Square, where crowd of more than 1,000 people cheered as the Prince arrived. Women wearing elaborate hats leant from the first-floor windows of India House opposite the square, which was established in 1730.

Harry officially named the garden before holding a private meeting with families of Americans and the 67 Britons killed on September 11.

Camilla Hellman, president of the British Memorial Garden Trust, is an old hand at royal visits — The Princess Royal, the Prince of Wales and the Duchess of Cornwall, and the Duke of York have all visited the garden, which is replete with London-style bollards, paving from Scottish and Welsh quarries and benches part-made in Northern Ireland.

Ms Hellman was thrilled to see the Prince. “The fact that Prince Harry’s been able to join us when we’re naming the park means a great deal to us, it gives it added significance,” she said. As part of the ceremony Harry planted a tree called a Magnolia Elizabeth in the park.

The Prince’s escapades have made headlines in the US press in the past, including his 2005 apology for wearing a Nazi swastika armband to a costume party. The New York Post, which dubbed him the Party Prince, usually prefaces his name with the words “bad boy” and references to his “party-hearty lifestyle”.

New Yorkers admired his mother, the Princess of Wales, and associate him with her love of socialising and ability to touch ordinary people. David Patrick Columbia, the co-founder of NewYorkSocialDiary.com, a website that chronicles the city’s rich and powerful people at play, expected Harry to receive a rapturous welcome.

“He’s young, he’s nice-looking, he acts like a devil-may-care kind of kid,” Mr Columbia said. “People adored Diana here and he's her son; she seemed real and one gets the impression that he’s like his mother.”

The Prince's soldiering background, in which he deployed alongside US forces in Afghanistan, also endears him to New Yorkers.

After the memorial garden, the Prince, who is training to be a helicopter pilot, was driven to a Veterans’ Affairs Medical Centre in Manhattan where, joined by Iraq and Afghanistan veterans, he toured the post-traumatic stress disorder clinic and tested some prosthetic limbs.

Joe Townsend, 21, a British soldier who lost both legs after stepping on a Taleban anti-tank mine in Helmand Province last year, accompanied the Prince on his trip to New York.

In case the Prince should find the temptations of the city that never sleeps too strong, the British Consulate organised a private reception for him with British business interests in the evening, before he went to a dinner with “family friends”.

Harry is likely to be disappointed tomorrow, however, if he expects the 2009 Veuve Clicquot Manhattan Polo Classic, held on Governors Island, a ferry-ride from Manhattan, to be a social scene equivalent to that of the UK.

Veuve Clicquot is ferrying in 400 guests for the match, including the actresses Kate Hudson and Chloe Sevigny and rapper Kanye West.

Mr Columbia warns that polo in the US does not attract a great deal of interest outside those that can afford to play and their family and friends. But the match is for a good cause: Sentebale, a charity founded by Harry and Prince Seeiso of Lesotho to help the African nation’s vulnerable children.

Harry will have to miss the after-party tomorrow night at Pink Elephant, a Manhattan nightclub popular with starlets and anyone else willing to pay the $20 door charge and brave the selective entry policy. The Prince was booked on a scheduled red-eye straight back to London.

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