URUMQI -- Authorities in Northwest China's Xinjiang Uygur autonomous region are thoroughly investigating a fatal high rise fire and have vowed to hold those suspected of dereliction of duty accountable.

The fire broke out at around 7:49 pm Thursday at a high rise residential building in Tianshan district in Urumqi, the regional capital, leaving 10 people dead and nine injured.

A joint investigation team has been set up to further look into the cause of the fire, said Mamtimin Hadir, mayor of Urumqi, at a press conference held Friday night.

On behalf of the municipal Party committee and the municipal government, the mayor expressed deep condolences to the victims, extended sympathy to the bereaved families, the injured and their families, and apologized to the people of the whole city.

People who are found to be negligent in their performance of duties before and during the accident must be held accountable, he said.

Medical assistance and treatment were immediately provided after the fire broke out and the injured are now in safe conditions, the mayor said.

A total of 109 firefighters and 23 fire engines were sent to the scene where the fire spread quickly and trapped many residents in their apartments, said Li Wensheng, an official with the city's firefighting department. It was put out at around 10:35 pm Thursday.

Li said narrow streets around the neighborhood where the building is located had made it difficult for large fire engines to approach to extinguish the blaze.

An initial investigation found that the fire might be caused by a plugboard in a bedroom on the 15th floor of the building.