Country hit by heavy rains as powerful typhoon sweeps north towards Taiwan.
However they could could not confirm whether this caused the accident.
Rescue workers said it could take weeks to remove the rocks to get to the bodies and none had been found so far.
Nguyen Tan Dung, the Vietnamese prime minister, sent condolences to families of the victims and has ordered an inquiry into the cause of accident, state television network VTV reported.
Hoang Trung Hai, Vietnam’s deputy prime minister, was sent to the province to oversee the search operation, the network said.