CHENGDU - Eleven people were injured, including four seriously, in an explosion that has ripped through an office building in Southwest China's Sichuan province, local authorities said Thursday.

The accident occurred around 2:50 pm Thursday at the second floor of a China Mobile branch building in Nanjiang county, said the county's governor Li Shanjun, who is organizing rescue work at the scene.

An initial investigation indicated that the blast might be caused by natural gas leak, Li said.

No death has been reported so far, and the injured have been sent to the People's Hospital of Nanjiang, according to Li.

Witnesses said the building's first three floors were severely damaged, and the fourth to eighth floors were also damaged by different degrees.