A PILOT has died and another was seriously injured after a suborbital passenger spaceship belonging to billionaire Sir Richard Branson's space tourism venture crashed during a test flight.

The co-pilot was killed and it is understood the pilot, who ejected, was injured and taken to a local hospital after Virgin Galactic's SpaceShipTwo rocket came down in the Mojave Desert in California.

The explosion scattered debris across a two-mile swathe of the desert and came after the plane was released from its WhiteKnightTwo carrier aircraft.

The identities of the pilots have not yet been released. George Whitesides, chief ­executive and president of Virgin Galactic, said they were employed by the ­company's partner business Scaled Composites.

An eyewitness reported that the craft exploded in flight after ignition.

A company spokesman said the rocket had "suffered a serious anomaly".

Television footage of the crash site showed wreckage of the spacecraft lying in two large pieces on the ground.

Local sheriff Donny Youngblood said the rocket was in several pieces on the ground, adding there was "one person who was obviously deceased immediately".

He said the other pilot appeared to have major injuries.

Stuart Witt, chief executive officer of Mojave Air and Space Port, called the incident "very unfortunate" and said his thoughts and prayers were with the families of those involved.

He added: "When we have a mishap from the test community, we find the test community is very small, and we are human, and it hurts."

Mr Whitesides, chief executive and president of Virgin Galactic, added: "Space is hard, and today was a tough day. The future rests in many ways on hard, hard days like this, but we believe we owe it to the folks who were flying these ­vehicles ... to understand this and to move forward, which is what we'll do.

"We are going to be supporting the investigation as we figure out what happened today. We are going to get through it."

Sir Richard said his thoughts were with all those at Virgin Galactic and Scaled Composites after the crash, adding: "Thanks for all your messages of support. I'm flying to Mojave immediately to be with the team."

He was expected to arrive this morning.

During the nine months since the previous rocket-powered test in January, Virgin Galactic switched the fuel mixture of SpaceShipTwo from a rubber-based compound to a plastic- based mix — in hopes that the new formulation would boost the hybrid rocket engine's performance. It had previously been tested on the ground.

It was designed to be carried into the air by the WhiteKnightTwo jet and then released before igniting its rocket to travel into space, before returning to Earth as a glider.

A Virgin Galactic spokesman said: "We will work closely with relevant authorities to determine the cause of this accident and provide updates as soon as possible. Our first concern is the status of the pilots."

Virgin Galactic has four pilots working on the SpaceShipTwo rocket. Its chief test pilot is Scot Dave Mackay, who joined up five years ago.

More than 800 people have paid or put down deposits to ­eventually fly in space, including Hollywood stars Angelina Jolie, Brad Pitt and theoretical physicist Stephen Hawking.

Each passenger has been assured they can have a refund at any time.

Others who have signed up for the trips include comedian Russell Brand - who was bought a ticket by his ex-wife Katy Perry for his 35th birthday - and actors Ashton Kutcher, ­Leonardo DiCaprio and Kate Winslet.