A Virgin Galactic space tourism rocket exploded during a test flight today, killing one pilot and seriously injuring another while scattering wreckage in Southern California's Mojave Desert, witnesses and officials said.
The company founded by British billionaire Sir Richard Branson would not say what happened other than that it was working with authorities to determine the cause of the "accident".
"During the test, the vehicle suffered a serious anomaly resulting in the loss of SpaceShipTwo," Virgin Galactic tweeted.
Ken Brown, a photographer who witnessed the crash, told the Associated Press that SpaceShipTwo exploded after a plane designed to take it to high altitude released it and the craft ignited its rocket motor.
He said the wreckage fell in the desert north of Mojave Air and Space Port, where the test flight originated. The area is about 193km north of central Los Angeles.
There is one fatality and one major injury, California Highway Patrol Officer Jesse Borne said. One person parachuted out, he said.
SpaceShipTwo, which is typically flown by two pilots, was designed to provide a suborbital thrill ride into space before it returns to Earth as a glider.
Today's flight was the 55th for the spaceship, which was intended to be the first of a line of craft that would open space to paying civilians. At 60ft (18m) long, SpaceShipTwo features two large windows for each of up to six passengers, one on the side and one overhead.
Virgin Galactic - owned by the Virgin Group and Aabar Investments PJS of Abu Dhabi - sells seats on each prospective journey for 250,000 US dollars, with full payment due at the time of booking. The company says that "future astronauts", as it calls customers, have visited Sir Richard's Caribbean home, Necker Island, and gone through G-force training.
Sir Stephen Hawking, Justin Bieber, Ashton Kutcher and Russell Brand are among the celebrities to sign up for flights. Virgin Galactic reports taking deposits totalling more than 80 million US dollars from about 700 people.
A related venture, The Spaceship Co, is responsible for building Virgin Galactic's space vehicles.
During testing for the development of a rocket motor for SpaceShipTwo in July 2007, an explosion at the Mojave spaceport killed three workers and critically injured three others.
A California Division of Occupational Safety and Health report said the blast occurred three seconds after the start of a cold-flow test of nitrous oxide - commonly known as laughing gas - which is used in the propulsion system of SpaceShipTwo. The engine was not firing during that test.
Today's accident was the second space-related explosion this week.
On Tuesday, an unmanned commercial supply rocket bound for the International Space Station exploded moments after lift-off from a launch site in Virginia. No injuries were reported in that accident, which drew criticism over Nasa's growing reliance on private US companies in this post-shuttle era.
Virgin Galactic planned to launch space tourism flights from the quarter-billion-dollar Spaceport America in southern New Mexico once it finishes developing its rocket ship.
Christine Anderson, executive director of the New Mexico Spaceport Authority, did not want to comment on the events unfolding in the California desert oday or what effect they might have on Spaceport America and the future of commercial space travel.
Virgin Galactic is in line to be the main tenant at the spaceport that was built specifically to launch paying customers into space, a dream of Sir Richard. His company has repeated pushed back the timetable for when the $250,000 flights were to begin, pointing to delays in development and testing of the rocket ship.
Taxpayers footed the bill to build the state-of-the-art hangar and runway in a remote stretch of desert in southern New Mexico as part of a plan devised by Sir Richard and former New Mexico Governor Bill Richardson. Critics have long challenged the state's investment, questioning whether flights would ever get off the ground.
SpaceShipTwo is based on aerospace design maverick Burt Rutan's award-winning SpaceShipOne prototype, which became the first privately financed manned rocket to reach space in 2004.
Commercial development has been slower than expected. When Virgin Group licensed the technology from Microsoft co-founder Paul Allen, who funded about $26 million for SpaceShipOne, Sir Richard envisioned operating flights by 2007.