This was a rental vehicle hybrid, while driving on a highway, the vehicle first developed a flat tire. Afterward, while the vehicle was in motion, smoke appeared and the vehicle caught fire spontaneously. There was no collision or impact of any kind. The driver pulled over and all passengers exited safely. The fire spread very rapidly and it's a total loss. The fire department responded and extinguished the fire. The fire appears to have originated in the hybrid battery area. The were no warnings. Safety risk: the fire occurred while vehicle was moving on a public highway with occupants inside, and spread very quickly after stopping. The Highway Patrol attended the scene and a police report was filled, incident documented. I'm reporting this as a serious safety concern.