Sir Richard Branson, the founder of Virgin Group, has pledged to "persevere and move forward" after the crash of SpaceShip Two spacecraft that killed a pilot and served a severe setback to the nascent space tourism industry.

Branson is on his way to Mojave where SpaceShip Two, the flagship space venture of the British billionaire, crashed during a test flight.

The cause of the crash remains unknown at this point.

The company said the craft experienced a "serious anomaly" during its 35<sup>th test flight while it was cruising above California's Mojave Desert, north of Los Angeles.

"Everyone at Virgin Galactic, The Spaceship Company and Scaled Composites is deeply saddened by today's events. All our thoughts are with the families of everyone affected by this tragic event, and we are doing everything we can to support them," Branson said in a blog post.

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

White Knight Two, the aircraft from which the SpaceShip Two was launched at an altitude of about 50,000 feet, returned to ground safely. The spacecraft suffered a mid-air explosion shortly after it peeled away from the aircraft.

Television images showed the debris scattered over a large area in the desert. The National Transportation Safety Board is set to begin investigation into the incident on Saturday, 1 November, and the probe is likely to take several days.

Both the pilots, whose identities have been withheld by the company, were employed by Scaled Composites, which designed the spaceship. The craft is designed to carry up to six passengers to nearly 100km above earth to experience the space for few minutes before returning.

"Space is hard, and today was a tough day. We are going to be supporting the investigation as we figure out what happened today, and we are going to get through it. The future rests in many ways on hard, hard days like this," Virgin Galactic CEO George Whitesides said in a statement.

The crash is bound to raise serious concerns for Virgin Galactic and could even be a public-relations nightmare apart from being a major blow to the space tourism industry as a whole.