Fans began lining up outside London's O2 Arena on Wednesday to buy tickets to Michael Jackson's 50 upcoming concerts. Jackson will return to the stage in July, and his concerts will run until next February. (Akira Suemori/Associated Press)

Fans had been waiting in line since Wednesday. And within hours of London's O2 Arena box office opening Friday, they snapped up about 500,000 tickets, selling out Michael Jackson's 50-concert comeback.

Another 360,000 advance tickets had been sold earlier this week.

Tickets for the "This Is It Tour" concerts — all at the 20,000-seat O2 venue — were limited to four per household. They were priced between $89 and $133 for general admission, and up to $1,100 for VIP seats.

They are now being advertised for thousands of dollars on Internet auction sites.

The concerts begin in July and run until next February. Jackson has said they will be his "final curtain call."

Unexpectedly popular

The King of Pop originally announced that he would do 10 shows, but promoters added another 40 dates because of the huge demand.

Randy Phillips of concert promoters AEG Live told BBC Radio that a pre-registration program had been so successful that he asked Jackson if he would do more shows.

"It wasn't anticipated," Phillips said.

Organizers said the tour has become the fastest-selling in history, with 33 seats sold each minute.

And despite what Jackson has said about the shows being his last in London, there is speculation that they could be part of a world tour.

The 50-year-old singer, who has won 13 Grammy awards and sold more than 750 million albums, hasn't had a major tour since 1997 or released a new album since 2001.

He withdrew from public life after being acquitted of child molestation charges in California in 2005.