Updated 2.49pm: The pilot injured in a Virgin Galactic test flight crash that killed his colleague is alert and talking.

Peter Siebold, the director of flight operations at Scaled Composites, was piloting SpaceShipTwo when it crashed in the Mojave desert in California on Friday.

His co-pilot Michael Alsbury was killed when the craft suffered what the firm called a serious anomaly.

Officials from the National Transport Safety Board (NTSB) have started their investigation into what caused SpaceShipTwo rocket, which had been under development at the Mojave Air and Spaceport, to come down.

More than a dozen investigators have been assigned to determine what went wrong.

Christopher Hart from the National Transport Safety Board says the nature of the flight should provide clues.

"This was a test flight and test flights are typically very well documented in terms of data and we may get some video feed, we should have lots of evidence that will help us with the investigative process."

Sir Richard Branson says he is determined to help authorities find out what caused the crash but likened the incident to the early days of flight.

Branson pledges to continue with space tourism

An emotional Sir Richard Branson has promised he'll get to the bottom of what went wrong on the Virgin Galactic spaceship.

Sir Richard has arrived at the Virgin Galactic base in the Mojave Desert.

"We do understand the risks involved and we're not going to push on blindly.

"To do so would be an insult to all those affected by this tragedy.

"We're going to learn from what went wrong."

Reporters asked Sir Richard about his future plans for Virgin Galactic.

"We owe it to our test pilots to find out exactly what went wrong and once we've found out what went wrong, if we can overcome it, we'll make absolutely certain that the dream lives on."