After weeks of hype This was, finally, It. Michael Jackson's posthumous curtain call, shown simultaneously in 18 different countries around the world.

Thousands of fans stayed up late, got up early and took time out from work to watch the premiere of This is It, the film made from 100 hours of rehearsals for the King of Pop's aborted London concert.

Hundreds of fans gathered outside the Nokia theatre in Los Angeles, the location of many of Jackson's rehearsals and his high profile public memorial, where the premiere was anchored.

Across the Atlantic, hundreds more gathered at a simultaneous opening in Leicester Square, in London, while another 150,000 fans from Brazil to Australia watched the LA event live on the internet.

Screenings of the film, described by its director Kenny Ortega as "a story of a master of his craft," were also held in 15 other cities including Seoul, Johannesburg and Berlin ahead of its formal release on Wednesday .

The film star Will Smith and the singer Jennifer Lopez joined Jackson's brothers in Los Angeles, although his three children, his mother and sisters were not seen at the premiere.

Jermaine Jackson told reporters: "You are going to see preparations for what would have been one of the greatest shows ever." However, he admitted: "You are going to see him going through the motions, not giving 100 per cent."

The film shows an enthusiastic Jackson meticulously crafting his moves and performing some of his most beloved hits for the 50 shows which had been planned for London's O2 Arena in July.

No critics have seen it, but Sony — which paid $60 million (£36.7m) for the film rights — showed a 12-minute clip to entertainment journalists last week.

Elizabeth Taylor, a longtime friend of the pop star, posted on Twitter: “It is the single most brilliant piece of filmmaking I have ever seen. It cements forever Michael’s genius in every aspect of creativity.”

In London, fan John Taylor said that he had travelled 70 miles to be at the premiere. "I've been a fan for over 30 years," said Mr Taylor, 38, who bought tickets for the first and last of Jackson's London shows. "The man's a legend."

Jackson was putting the finishing touches to the show when he died suddenly on June 25, aged 50. The Los Angeles County coroner has ruled the death a homicide, caused primarily by the powerful anesthetic propofol and another sedative. Jackson’s personal physician, Dr Conrad Murray, has not been charged with a crime but is the focus of the police investigation.

Video footage from the rehearsals had been intended to help organisers critique the show and was never intended for public viewing.

However more than 800,000 tickets have been sold for the concerts, with organizers promising one of the "most expensive and technically advanced" live shows ever.

In the US, the online ticket seller Fandango.com said that more than 1,000 showings of the movie were sold out and so far This Is It was the number three top-selling advance ticket of 2009.

Global box office estimates vary from more than $600 million over its planned two-week run down to $100 million.

A group of diehard Jackson fans launched their own on-line counter campaign, urging devotees of the singer to boycott the movie, and claiming it hides the truth about his final days.

The group claims on its website — This-Is-Not-It — that the movie attempts to mask Jackson's physical frailty as he maintained a punishing schedule of rehearsals. "In the weeks leading up to Michael Jackson's death, while this footage was being shot, people around him knew that he looked like he might have died," the group said. "Those who stood to make a profit chose to ignore it."

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