Engine Knocking Noise problems of the 2000 Lexus GS300

While car was parked in the garage it was trying to start up on it's own with no keys. The dash lights were blinking and the car was making a loud cranking, banging noise and we could smell the smoke. After lifting up the hood we could see the smoke coming from the engine and it was still trying to crank up. Smoke begin to fill the garage and it was getting worse. We were finally able to put out the fire with the extinqisher and were able to remove the battery to get the car to stop trying to start up. What would cause such a dangerous thing to happen. Car is still in the garage at this time not sure what to do with it because I am not sure of the engine damage the fire caused. Is this some kind of electrical malfunction?.