At least seven people died on Saturday when a bus carrying 19 passengers overturned on a mountainous road in Vietnam's northern province of Yen Bai, state-run media reported.

The 29-seat bus carrying a charity group was travelling downhill when it flipped and was crushed, according to Vietnam News Agency.

Rescue teams pulled 10 survivors from the wreckage, while others remained trapped as of 10:30 am (0330 GMT) as heavy equipment was deployed to cut through the vehicle, Hoang Anh Tuan, chairman of Phinh Ho commune, told VNA.

Tuan said the crash was likely caused by brake failure.

Calls to authorities of Yen Bai province and Phinh Ho commune went unanswered.

Police, military units, local officials and residents were mobilised for rescue efforts, while authorities said an investigation into the cause of the accident was ongoing, according to VNA.