HANOI, Jan. 17 (Xinhua) -- Four people were killed and one injured after a passenger bus crashed into a roadside drainage culvert and overturned in Vietnam's northern mountainous province of Son La early Saturday morning, local media Voice of Vietnam reported.
The accident occurred at around 4:15 a.m. while a 36-seat passenger bus was traveling from Hanoi to Son La.
At the time of the accident, the bus was carrying about 18 people, including 14 passengers, two drivers and two bus attendants.
Preliminary checks showed that the driver tested negative for alcohol and drugs, authorities said.
The area was experiencing rain and fog, making the road surface slippery at the time of the accident.
The case is under further investigation. ■