LAS VEGAS — A driverless shuttle bus has crashed less than two hours after it was launched in Las Vegas.

Police say no injuries were reported in the Wednesday crash between the self-operating vehicle and a semi-truck. It’s not yet clear what caused the wreck.

Officials had hosted an unveiling ceremony to promote what they described as the nation’s first self-driving shuttle pilot project geared toward the public.

The oval-shaped shuttle that can transport up to 12 passengers has an attendant and computer monitor, but no steering wheel and no brake pedals. It uses GPS, electronic curb sensors and other technology to make its way.

Before it crashed, dozens of people had lined up in downtown Las Vegas to get a free ride.

Police say the crash blocked traffic near the Fremont Street entertainment district.