Bill Clinton met actor Kevin Spacey

Actors Hugh Grant, Whoopi Goldberg and Kevin Spacey joined De Niro and the statesmen on the podium to help boost the area's economy and spread a wider message.

Film could help foster understanding and tolerance around the world, Mr Mandela told a crowd.

The festival is expected to attract 50,000 people and features the US premi�res of the new Star Wars movie and Grant's latest film, About A Boy.

De Niro, who has lived in Tribeca for 20 years, was planning a festival before 11 September, but said it took on extra significance after the attacks.

Mr Mandela said that the world had watched with admiration as the residents of New York rallied to cope with the tragedy.

'Reach out'

"The producers, directors and actors of films have in their hands a powerful and evocative tool for fostering understanding, and through that, tolerance in the world," he said.

The About A Boy premi�re took place on Wednesday

"It is furthermore a medium that is not bound in its reach. It can reach out to all strata and sectors of society and across national and linguistic boundaries."

Mr Mandela, 83, received four standing ovations as he spoke on the steps of City Hall.

New York Mayor Michael Bloomberg said the former South African president told him that thinking about his favourite film scenes helped him through the "unspeakable loneliness" of imprisonment.

Sitting on the same stage as the politicians, Hugh Grant joked that he had been accused of being a lightweight actor in his time.

"And I can assure you I have never felt more lightweight than I do standing on this platform, in this company," he said.

150 films will be shown over five days

But he said it was a "massive honour" to be opening the event.

"It's truly very important, especially for New York, and I love New York," he said.

The US premi�re of About A Boy took place on Wednesday after becoming the most successful British film of the year in the UK.

Star Wars: Episode II - Attack of the Clones gets its premi�re on Sunday, 12 May, four days before it goes on release at cinemas around the world.

More than 150 films will be shown over the five days of the festival.