LOS ANGELES - Virgin Galactic's SpaceShipTwo craft crashed Friday after getting into difficulties during a test flight over California and the fate of two pilots is unknown, the company said.
"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.
The craft, which is still in its test phase and which normally carries two pilots, had been carried aloft on a bigger aircraft known as WhiteKnightTwo and then released for a test of its rocket engine.
WhiteKnightTwo had taken off normally from California's Mojave desert, and been released normally, 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."
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 SS2.
SpaceShipTwo 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.
Friday's incident is the second involving a space craft this week, after an unmanned Orbital Science rocket exploded on Tuesday six seconds after launch on a resupply mission to the ISS.
Copyright Agence France-Presse, 2014