London  - Tickets for Michael Jackson's This Is It comeback tour in Britain were sold out within hours of going on sale Friday even after the number of gigs was increased to 50, organizers said.

Organizers AEG Live said 750,000 tickets had been sold for the concert series due to start on July 8, reflecting a "truly amazing level of interest."

The US superstar announced in London last week that he would give an initial 10 concerts from July in what he called his "curtain call" in the British capital.

However, following strong pre-sale demand, organizers have added another 40 dates, prolonging the Jackson series into February 2010.

They were sold out within hours after fans from around the world had queued through the night outside the venue in London where they will be staged.

Thousands jammed phonelines as tickets were sold at a rate of 40,000 per hour.

"This was undoubtedly the busiest demand for tickets for an event which we have ever experienced," said Chris Edmonds of distributors Ticketmaster UK.

Fans travelled from Japan, Asia, Latin America, the Gulf states and European countries to purchase tickets, priced between 50 pounds (70 dollars) and 75 pounds.

However, they were being offered Friday for thousands of pounds on auction website eBay.

Jackson, who has returned to the United States for rehearsals, is said to be "ecstatic" about the response.

The concerts will be staged in London's O2 Arena, the former Millennium Dome, in the revamped docklands in east London, which can hold 20,000 people. (dpa)