Virgin Galactic's SpaceShipTwo at a Virgin Galactic hangar at Mojave Air and Space Port in Mojave.(AP)
Virgin Galactic's first commercial spacecraft crashed Friday during a test flight over California, scattering debris over the desert and leaving the fate of two pilots unknown, the company said.
Television images showed parts of SpaceShipTwo, a test vehicle flying to the edge of space, scattered amid brush in the desert east of Mojave, a few hours' drive northeast of Los Angeles.
The incident is second disaster involving a US spacecraft this week, after an unmanned Orbital Science rocket exploded on Tuesday six seconds after launch on a resupply mission to the ISS.
"During the test, the vehicle suffered a serious anomaly resulting in the loss of SpaceShipTwo. Our first concern is the status of the pilots, which is unknown at this time," the firm said in a tweet.
"We will work closely with relevant authorities to determine the cause of this accident and provide updates as soon as we are able to do so," it said.
Officials were due to give a press conference at 2:00 pm (2100 GMT) to release more details of the accident, according to the KGET local TV station.
The spaceship had been carried aloft on a bigger aircraft known as WhiteKnightTwo and then released for a test of its rocket engine above the Mojave desert, in what was the 35th such flight.
"SpaceShipTwo has been released by WhiteKnightTwo, and is now flying freely," the firm wrote in a blow-by-blow account of the flight, adding: "Ignition! SpaceShipTwo is flying under rocket power again."
The next tweet announced the "anomaly", followed by the series confirming the crash. The company added that WhiteKnightTwo had landed safely after the accident.
More than 500 people have already reserved seats -- and paid a deposit on the $200,000 ticket price -- for a minutes-long suborbital flight on SpaceShipTwo, which can carry six passengers.
It is the commercial version of SpaceShipOne, the first private spacecraft to reach the edge of space in 2004, and which is now on displace at the National Air and Space Museum in Washington.
Private companies are rushing to fill the gap left by NASA, which ended its 30-year shuttle program in July with the completion of the final Atlantis mission to the International Space Station (ISS).