One One person is dead and another injured after a Virgin Galactic suborbital rocket plane crashed on a powered test flight over California.
The tragedy occurred after SpaceShipTwo fired its rocket motor following a high-altitude drop from Virgin Galactic's WhiteKnightTwo mothership.
California Highway Patrol reported one fatality and one "major injury" after Friday's incident.
Wreckage from the crashed aircraft in the Mojave Desert
Virgin Galactic, part of Richard Branson's Virgin Group, aims to begin tourist flights to the edge of space next year.
The company said in a statement to Sky News: "Virgin Galactic's partner Scaled Composites conducted a powered test flight of SpaceShipTwo earlier today.
Dead As Virgin Galactic Spaceship Crashes
The tragedy over the Mojave Desert comes as Virgin Galactic was preparing to begin tourist flights to the edge of space next year.
"During the test, the vehicle suffered a serious anomaly resulting in the loss of the vehicle.
"The WhiteKnightTwo carrier aircraft landed safely. Our first concern is the status of the pilots, which is unknown at this time.
"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 is the second disaster involving a US spacecraft this week, following the explosion of a private company's unmanned rocket on Tuesday six seconds after launch on a resupply mission to the International Space Station.
TV pictures on Friday showed wreckage from the crashed Virgin Galactic aircraft in the Mojave Desert.
Parachutes were reportedly spotted in the air. SpaceShipTwo is usually flown by two pilots.
The craft was testing a redesigned rocket motor as it made its first powered flight since January.
The company live-tweeted the test flight, posting: "Ignition! #SpaceShipTwo is flying under rocket power again. Stay tuned for updates."
The next tweet said: "#SpaceShipTwo has experienced an in-flight anomaly. Additional info and statement forthcoming."
The rocket plane, which was attached to the underside of WhiteKnightTwo, took off at 9:19am local time (4:19pm GMT) from the Mojave Air and Space Port in California.
It is the commercial version of SpaceShipOne, the first private spacecraft to reach the edge of space in 2004, now on display at the National Air and Space Museum in Washington DC.
Virgin Galactic aims to become the world's first commercial "spaceline", sending customers willing to pay $250,000 (£156,000) for a short journey into zero gravity and a glimpse of the planet from the edge of space.
The company previously said it has accepted more than $80m in deposits from about 680 people who hope to be among the first space tourists.
Actors Leonardo DiCaprio and Ashton Kutcher and singer Justin Bieber are said to have signed up.
After launching from New Mexico, it is envisaged that each spaceship will take six passengers on a journey of between two and three hours just over 62 miles (100km) from Earth.
Eventually, Branson hopes to build a hotel in space.