Investigators say there is a massive search site after a Virgin Galactic spaceship making a test flight in California crashed, killing one pilot and badly injuring the other.
The company's head, Sir Richard Branson, said he was on the way to the area to be with his team, the BBC reported.
The space tourism craft was flying a manned test when it experienced what the company described as "a serious anomaly".
It was undergoing its first powered test flight since January over the Mojave Desert, north of Los Angeles.
Television images shot from a helicopter showed what appeared to be wreckage bearing the Virgin logo, and officials said debris was strewn over a large area.
SpaceShipTwo is carried aloft by a jet, then launched into sub-orbit.
In a statement, Virgin Galactic said the "vehicle suffered a serious anomaly resulting in the loss of SpaceShipTwo".
Kern County Sheriff's spokesman told Reuters the craft's co-pilot was killed, while the pilot ejected and was seriously injured.
Ken Brown, a photographer who witnessed the crash, told the Associated Press the craft exploded after it was released from the plane.
The aircraft that held the spaceship, known as White Knight 2, landed safely, Virgin Galactic said.
Officials with the National Transportation Safety Board will soon begin work to investigate the cause of the accident, which will likely take several days.
Virgin Galactic chief executive George Whitesides said the company would support the investigation as it figured out what happened.
"The future rests in many ways on hard days like this but we believe we owe it to the folks who were flying these vehicles as well as the folks working so hard on this to understand this and move forward."
Virgin Galactic has been a front-runner in the nascent space-tourism industry and Sir Richard said earlier in October he expected to see the craft make it to sub-orbital space within a few months.
More than 800 people have already paid or put down deposits for a trip on SpaceShipTwo, which costs about $200,000 per person.
It is the second accident this week by a US space company.
On Wednesday, an unmanned Orbital Sciences Antares rocket exploded 15 seconds after lift-off, destroying a cargo ship bound for the International Space Station.