An air-conditioned, gas-fuelled bus burst into flames after a short circuit in the engine compartment and was destroyed on inbound Sukhumvit Road in the Ekkamai area on Tuesday morning.
Due to the quick thinking of the crew, all passengers were whisked quickly off the bus and were uninjured.
The BMTA was later eager to point out the bus was owned by a concessionaire and although also made in China it was not built by the same company that supplied the natural gas fuelled buses on the city's own bus fleet.
The No.40 bus, on the Lam Salee-Southern Bus Terminal route, caught fire in front of the Gateway shopping centre in Klong Toey district about 9.30am.
It blocked the road, causing heavy traffic congestion.
Firefighters called to the scene quickly extinguished the flames.
Police said the bus ran on compressed natural gas and the fire started in the engine compartment, possibly caused by an electric short circuit there.
Prayoon Chuaikaew, acting director-general of the Bangkok Mass Transit Authority, later confirmed the fire was caused by a short circuit in the engine compartment.
Bus staff were quick enough to evacuate passengers so that no one was hurt.
The bus belonged to concessionaire Pornpin Transport Co. It ran on compressed natural gas and was made in China under the Golden Dragon name, he said.
Officials of the BMTA and the Land Transport Department would check all Golden Dragon buses serving route 40 on Friday to ensure they were safe.
Mr Prayoon said the BMTA itself was operating 100 natural gas-fuelled buses built by Bonluck, not Golden Dragon.