MOJAVE, Calif. (AP) - An explosion on Thursday at a Mojave Desert airport left two people dead and four others injured, authorities said.

It was not immediately clear what caused the blast, which happened around 2:45 p.m. in a remote section of the Mojave Air and Space Port, said Tony Diffenbaugh, an inspector with the Kern County Fire Department.

The airport is home of Scaled Composites, the builder of SpaceShipOne, the first private manned rocket to reach space. The company is developing a successor for the new space tourism business Virgin Galactic.

It wasn't immediately clear whether any of the company's buildings or equipment were involved.

Aerospace designer Burt Rutan, who heads Scaled, told The Associated Press he had no information and was heading to the scene.

Wreckage of equipment and vehicles could be seen in an overhead view of the site broadcast by a KCAL-TV news helicopter. A sign on a truck behind a bunker had the name Scaled.

``Reports are two fatalities and at least four critical injuries,'' said Kern County fire Capt. Doug Johnston, who was not at the scene.

Kern County fire crews and bomb experts were en route to the scene, where there was concern that airport personnel could be exposed to hazardous materials, authorities said.

A call seeking comment from the airport manager was not immediately returned.

07/26/07 19:37 © Copyright The Associated Press. All rights reserved. The information contained In this news report may not be published, broadcast or otherwise distributed without the prior written authority of The Associated Press.