Michael Jackson will now play 50 dates at London's O2 arena, continuing his farewell residency well into 2010.
The 50-year-old has added new shows throughout the first two months of the year, ending on 24 February.
Some 360,000 pre-sale tickets have been sold so far and if all 50 dates sell out, Jackson will have sold a million seats for the run of shows.
Organisers say the This Is It tour has become the fastest selling in history, with 33 seats sold each minute.
Jackson is said to be "thrilled" by the response.
Randy Phillips of promoters AEG Live said: "Not only are these concerts unparalleled, these records will never be broken.
"We knew this was show business history, but this is a cultural phenomenon."
Pre-sale tickets for Jackson's first 10 dates sold out on Tuesday but some fans complained of "technical problems" trying to register online.
Ticketmaster director Chris Edmonds said demand was "unprecedented".
He added: "Unfortunately due to a technical issue, we were unable to facilitate all immediate ticket requests. Apologies to those fans who were unable to log on, but fans should keep on trying to purchase tickets."
Additional codes are being issued, the organisers said, with registration being dealt with on a first come, first served basis.
Tickets are only being sold to fans who have registered, with the rest of the seats going on sale to the general public from 0700 GMT on Friday.
Tickets for the Jackson shows are already being sold on the online auction website eBay.
Prices on the site range from £170 to £10,000, but tickets bought directly from the singer's website or Ticketmaster cost up to £75.
Jackson, who has won 13 Grammy awards, has said this will be the last time he will perform in the UK.
In August and September 2007, Prince played 21 concerts at the O2 arena together with a number of aftershows at its club venue, Indigo.
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