PERTH (AFP) - Thirteen children from Indonesia and Malaysia were taken to hospital after their bus rolled over and crashed into a ditch in Western Australia, police said Thursday.

The children, aged between 10 and 12, were heading with eight adults to Lake Leschenaultia for a camping trip on Wednesday evening when the driver appeared to lose control of the bus, which "careered into a drainage ditch".

"Three suffered injuries including suspected broken bones, and all were taken to hospital for observation," police said in a statement.

"Although the injuries are serious, they are not believed to be life-threatening."

Eight children remained in two Perth hospitals on Thursday in a stable condition.

Eight adults were also hospitalised, although their injuries were not known, with seven still being treated.

Investigators said they were looking into whether fog was a factor in the crash, which took place at Gidgegannup, some 40km east of Perth.

The children and adults were members of environmental groups E-ija in Malaysia and Tunas Indonesia, The West Australian newspaper said. The breakdown of nationalities was not immediately known.