Twelve people were killed and 30 others injured in two road crashes within four kilometres of each other in Surat Thani on Wednesday night and Thursday.

Police and rescuers were called about 7am on Thursday to an incident on Asian Highway 41.

They found a Toyota pickup truck with its front badly damaged next to a tree on the median.

Four people — two girls and two boys — were found dead at the scene. Three other adults were seriously injured and rushed to hospital, where they were pronounced dead.

A witness told police the truck had been travelling at high speed before swerving to avoid a minivan that was parked at the roadside to pick up some students, leading to the crash.

The crash occurred about 4 kilometres away from the site of a tour bus accident that killed five people and injured 30 on the same road on Wednesday night.

The bus carrying 37 people skidded off Asian Highway 41 and plunged into a roadside ditch at about 7.30pm on Wednesday.

The force of the crash killed five people at the scene and injured 30 others, three seriously. 

One passenger said he heard what sounded like the bus falling into a hole before it skidded off the road into the ditch dividing the road. It hit several trees.

The two bus drivers were held for questioning.