LUZHOU, Sichuan, Dec. 27 -- The identities of four victims of Thursday's blast in a shopping mall in Luzhou City in southwest China's Sichuan Province have been confirmed.

The explosion occurred around 10:40 p.m. Thursday at the Mo'erma shopping mall and flames soon spread to the ground and second floors, leaving four dead and another 40 injured, sources with the municipal government said Friday.

Three of of the four dead were local residents, and another one was from east China's Fujian Province.

Five of the injured people have been discharged from the hospital, and the rest remain hospitalized, authorities said.

An initial investigation shows that the blast was triggered by a natural gas leak, according to local work safety authorities.