At least 39 people were injured when a blast went off Friday morning at a rural bank in northwest China's Gansu Province, witnesses and the local government said.

The provincial government said six people were seriously wounded and another 33 suffered slight injuries. They were all being treated at the county hospital.

The government identified the accident as a case of "arson" in a press release issued at 11:30 a.m..

Blast went off at the Rural Credit Cooperatives in Tianzhu Tibetan Autonomous County in the city of Wuwei at around 8:30 a.m., when all the bank employees were having a meeting.

A witness who declined to be named said someone ignited a homemade "gasoline bomb".

He said he saw more than 10 people throwing themselves out of the window of the fourth-floor meeting room, while many others, with charred bodies and limbs, were carried out of the building on stretchers.

Police cordoned off the street for investigation shortly after the accident.

Tianzhu County is 128 km from Lanzhou, the provincial capital. A third of the county's 210,000 residents are Tibetans.