SpaceShipOne, piloted by 62-year-old South African-born Michael Melvill, reached an altitude of more than 330,000 feet (100 kilometers), jubiliant organizers said, citing two unofficial radar readings.

Official confirmation of the exact altitude reached by Melvill was expected later.

To win the 10-million-dollar Ansari X Prize, the same manned spacecraft must be sent into space twice in two weeks. SpaceShipOne's second flight is expected on Monday, again from the Mojave Desert in California.

SpaceShipOne ignited its rocket engines after being dropped from a specially adapted jet, named White Knight, at an altitude of some 47,000 feet (15 kilometers) and blasted off towards space.

Attaining speeds of up to Mach 3.5, the craft twisted like a corkscrew during a dramatic ascent to the fringes of space.

An organizer said there had been "unexpected maneuvers" and an "anomaly" in the operation but praised Melvill for retaining control. "He's the best pilot we could possibly have had," said the visibly operation official.

Melvill confirmed there was some unexpected roll but was elated after his run.

"Now that was fun," he said minutes after landing. "I really shot up. I didn't feel like I got a lot of rolling again like I did last time. But right up at the top I got a surprise when it really spun out and I did a little victory roll."

He said he aborted the flight, shutting down the engines 11 seconds ahead of schedule, when he realized he had reached the required altitude "with room to spare."

The White Knight jet carrying SpaceShipOne on its belly, took off from a Mojave Desert air base at 7:11 am (1411 GMT).

SpaceShipOne separated from the jet at around 8:09 am (1509 GMT) and successfully blasted off. The stubby rocket ship glided to a smooth landing in the Mojave desert at 8:34 am (1534 GMT).

Aviation pioneer Burt Rutan and his company Scaled Composites joined with Microsoft founder Paul Allen and his firm Vulcan to form the Mojave Aerospace Ventures team behind SpaceShipOne, which carried out a successful test flight on June 21.

The Ansari foundation put up the 10-million-dollar prize eight years ago to give the same impetus to space travel that the Orteig prize did to inspire Charles Lindbergh's first transatlantic flight in 1927.

The winner must carry the pilot and the equivalent weight of two passengers. Instead of lead weights, boxes of memorabilia and trinkets supplied by team members and sponsors -- who include major names such as candy maker M and M and soft drink 7UP -- will act as ballast.

There are 26 teams in contention for the Ansari prize but SpaceShipOne is the most advanced.

A Canadian team, Da Vinci, which has linked up with the world's biggest online gambling website, goldenpalace.com, plans to launch a manned rocket attached to a balloon at 90,000 feet (27,000 metres). The return to Earth would be with a parachute.

The Canadians had planned a trial run on October 2 but postponed it.

Rutan expects SpaceShipOne to attract a lot of investment to the sector, and that in a few years people will be able to buy tickets for sub-orbital flights.

The flight is taking place just two days after British tycoon Richard Branson announced a tie-up with Rutan to start a "galactic" airline aimed at eventual commercial space travel.

Rutan sat by Branson's side in London on Monday when the British founder of Virgin Atlantic Airways announced he had signed a 14 million pound (25 million dollar) accord with Mojave Aerospace Ventures to set up Virgin Galactic, the first company to offer trips into space for the general public.

The project will use technology based on SpaceShipOne and Branson has predicted the first flights could take place in three years.

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