CHENGDU - A blast in southwest China's Sichuan Province has left one person dead and 25 others injured, including three seriously injured, local authorities said Thursday.

The accident occurred around 3 pm Thursday on the second floor of a China Mobile branch building in Nanjiang county, the county's publicity department said in a statement.

An initial investigation indicated that the blast was caused by a natural gas leak, according to the statement.

The injured have been sent to two local hospitals.

A further investigation into the cause of the leak is underway.

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

Li Gang, party chief of the city of Bazhong, which administers the Nanjiang county, said a safety overhaul will be carried out in the city.