London - The This Is It comeback concert series announced by US superstar Michael Jackson in London last week is a sell-out despite 13 more shows having been added to the original 10 performances, organizers said Wednesday.

Organizers AEG Live said pre-sale demand for tickets had been overwhelming for the series, due to open at London's O2 Arena on July 8. It will now not finish before early September.

The pre-sale website had crashed repeatedly over the past few days, said the organizers, as demand grew from around the world.

Tickets for the concerts go on sale at www.michaeljackson onlive.com from March 13.

Jackson, 50, made a personal appearance at the O2Arena last Thursday to announce his combeack with what he said would be his "curtain call" in London.