XIAMEN - Forty-seven people died and 34 others were injured after a bus burst into flames on an elevated bus lane in Xiamen city in East China's Fujian province on Friday evening, authorities said.

The deadly bus fire is a "serious criminal case", investigators said.

A BRT (bus rapid transit) bus caught fire in the city of Xiamen at about 6:30 pm, said an official from the municipal government.

The fire broke out when the bus was 500 meters away from the Jinshan bus stop, the official added.

A bus is totally destroyed after a fire in Xiamen city, East China's Fujian province on June 7, 2013. [Photo/Xinhua]

A Xinhua reporter at the scene saw the charred frame of the bus perched on the viaduct about ten meters above the ground. Some witnesses said they heard explosions about ten minutes after the fire broke out.

The reporter said the fire occurred during the evening rush hour, when the city's BRT buses are usually packed with commuters.

A slightly injured passenger surnamed Yang said she was using her mobile phone when she smelled gasoline and saw another passenger smashing the window in an attempt to escape.

The fire spread quickly, she recalled.

Pictures allegedly taken by witnesses and posted online showed heavy smoke as the fire engulfed the bus, as well as survivors with burns on their arms and legs.

A nurse at the First Affiliated Hospital of Xiamen University said the hospital has admitted 17 of the injured, including three to the intensive care unit.

The cause of the fire is under investigation.