Organizers of the Led Zeppelin-headlined Ahmet Ertegun tribute concert on Nov. 26 have extended the registration deadline in the wake of "unprecedented demand" for tickets.

The ballot has now been extended from a midday Sept. 17 close, to midday Sept. 19, after the Web site set-up to handle ticket registrations received 89.5 million attempts in a 12-hour period on Thursday.

"We apologise to anyone who has so far been unable to access www.ahmettribute.com," comments promoter Harvey Goldsmith in a statement today. "This is due to unprecedented demand, the Web site has been receiving over five million hits per hour since the press announcement 24 hours ago. The service provider is doing their best to keep the site running and has moved it to a server on its own."

Since confirmation Wednesday of the one-off Led Zeppelin comeback at London's O2 Arena, the online service has had 80,000 requests each minute, at one point causing the system to crash, according to a spokesman.

Just 18,000 tickets, priced at £125 ($250) will be distributed to applicants on a lottery-basis, capped at two tickets per household.

Speaking at a press conference on Wednesday, Goldsmith admitted 852 corporate tickets, priced upwards of £1,000 ($2,000) each, would be held aside to cater particularly for interest in the U.S.

Zeppelin will play "all the big numbers" in a "meaty" set of roughly two hours, Goldsmith said. The Who's Pete Townshend, Bill Wyman and the Rhythm Kings, Foreigner's Mick Jones and Paolo Nutini will each perform 30-minute sets on the night.