Firefighters tackled the blaze after a bus caught light on its route and "explosions" were heard.
Herts Fire and Rescue had been called to Little Bushey Lane, near Chiltern Avenue in Bushey, at 5.45pm yesterday (June 10) with reports that a 306 bus was on fire.
Two fire engines were sent out, with crews finding the vehicle “well alight”, but everyone was safely off and no one was hurt.
Little Bushey Lane was closed while firefighters worked and they were able to extinguish it by 6.35pm.
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Punit Goyal, who witnessed the fire, said: “I saw a bus stopped and smoke coming out. Soon it caught fire at the back and suddenly it was huge and there were small explosions at the back, with glass windows exploding.
“The fire engines arrived promptly and doused it. They told me the driver had lost power while uphill and contacted fire department."
The road remained closed between Chiltern Avenue and Richfield Road this morning.
Footage from the scene shows firefighters using jet hoses to extinguish the bus, with flames clearly visible inside the vehicle.
The 306 bus runs on a partly circular route between Watford and Borehamwood.
