Thirteen students and eight adults from Malaysia and Indonesia were involved in a bus crash in Perth Hills on Wednesday night, which left two teachers and a volunteer injured.

Malaysian group leader, Mohd Fakri Bakri told Bernama that the students, including 10 from a primary school in Section 9, Shah Alam, were unhurt but shaken.

The three injured adults, all Malaysians, sustained broken limbs and were warded in a hospital overnight.

"The students are all fine and we have informed their parents," said Mohd Fakri said.

The students were on a bus about 7.40pm and heading to a campsite at Lake Leschenaultia, about 50km east of Perth, when it crashed.

The bus skidded and plunged into a ditch, about 40km east of Perth city.

Mohd Fakri said there was a heavy fog in the area at the time, which reduced visibility and might have contributed to the crash.

All passengers were taken to hospitals around the Perth metropolitan area for observation, while three who sustained injuries, including broken bones, are still in hospital.

Mohd Fakri said the Malaysians who arrived in Perth on Tuesday would return to Kuala Lumpur on Saturday. They are currently housed at Malaysia Hall in Perth.

Millennium Kids, the non-profit organisation which hosted the Malaysian and Indonesian students, said the youngsters were in Western Australia to attend a forum hosted by the Swan River Trust.

Millennium Kids chairman Rachael Cochrain said most of the students on the bus were from the Kuala Lumpur-based group, E-ijau, while three were from Tunas Indonesia, a youth environment organisation based in Surabaya, Indonesia.

Cochrain said the group was working closely with the Indonesian and Malaysian consulates to help the youngsters get in touch with their families.