Media playback is unsupported on your device Media caption The moment the craft exploded was captured by a photographer

Sir Richard Branson has vowed to continue his space tourism venture despite the fatal crash of a Virgin Galactic rocket ship in the US.

One pilot died and the other was badly injured when SpaceShipTwo exploded in California's Mojave Desert on Friday.

Investigators are on their way to the crash site, north of Los Angeles.

Sir Richard, founder of Virgin Group and long-time advocate of commercial space travel, said he was "shocked and saddened" but would "persevere".

Virgin had hoped to launch commercially in 2015. It has already taken more than 700 flight bookings at $250,000 (£156,000) each, with Mr Branson pledging to travel on the first flight.

'Serious anomaly'

SpaceShipTwo was flying its first test flight for nine months when it crashed shortly after take-off near the town of Bakersfield, California.

In a statement, the company said SpaceShipTwo experienced "a serious anomaly" after the craft separated from its launcher, an aircraft called WhiteKnightTwo.

WhiteKnightTwo landed safely.

It later emerged that the space craft was burning a new type of of rocket fuel never before used in flight, although officials said it had undergone extensive ground testing.

Sir Richard said Virgin Galactic would co-operate fully with the authorities involved in the investigation.

Officials with the US National Transportation Safety Board will begin their investigation on Saturday morning, which will probably take several days.

The Federal Aviation Administration is also investigating, officials said.

Media playback is unsupported on your device Media caption Eyewitness Ken Brown: "It burned for a time and then just exploded"

'Space is hard'

In a blog post, Sir Richard said everyone involved in the project was "deeply saddened".

"All our thoughts are with the families of everyone affected by this tragic event," he wrote.

He said that he was flying to California, describing it as "one of the most difficult trips I have ever had to make".

"Space is hard - but worth it. We will persevere and move forward together," he added.

George Whitesides, chief executive of Virgin Galactic, echoed Sir Richard's comments at a California news conference.

"The future rests in many ways on hard days like this, but we believe we owe it to the team to understand this and to move forward. And that is what we'll do."

Media playback is unsupported on your device Media caption Virgin Galactic ticket holder Jon Goodwin is confident it will be "perfectly safe"

Wreckage from the crash was scattered across the Mojave desert, north-east of Los Angeles. Police secured the site amid fears that some of the debris could be explosive.

Both pilots were employed by Scaled Composites, the company that designed the craft. One was pronounced dead at the scene while the other was transported to a local hospital in an unknown condition.

The spacecraft had been carried into the air by WhiteKnightTwo before being released at an altitude of 45,000 feet (13,700m) for a test of its rocket engine. It crashed shortly afterwards.

Celebrities including Justin Bieber, Ashton Kutcher and Leonardo Di Caprio are among those said to have signed up for the flights, the Los Angeles Times reports.

It was the second accident this week involving a commercial space company in the US.

On Tuesday, an unmanned supply rocket called Antares exploded shortly after its launch from Virginia. It was carrying cargo to the International Space Station.

David Shukman, BBC science editor

Image copyright Reuters

Even as details emerge of what went wrong, this is clearly a massive setback to a company hoping to pioneer a new industry of space tourism. Confidence is everything and this will not encourage the long list of celebrity and millionaire customers waiting for their first flight.

An innovative design combined with a new type of rocket motor make the development exceptionally hard. Despite an endless series of delays to its spacecraft, Virgin Galactic has over the years managed to maintain some very optimistic public relations and positive media coverage.

I interviewed Sir Richard Branson when he first announced the venture, and his enthusiasm and determination were undoubted. But his most recent promises of launching the first passenger trip by the end of this year had already started to look unrealistic some months ago.

This accident will delay plans even further. Space is never easy, and making it routine is even harder.

Will crash set back space tourism?