Three Malaysian schoolgirls have described the panic and shrieks of terror as their bus catapulted off a fog-cloaked Toodyay Road at high speed.
The party of 14 students aged between 10 and 12 and their chaperones were flung from their seats on Wednesday night when the hire bus they were travelling in veered into a ditch 2km west of Gidgegannup.
The Malaysian and Indonesian pupils - many enjoying their first visit to Australia - had been bubbling with excitement following an eagerly anticipated Millennium Kids environmental forum with Perth students earlier that day.
Passenger Fatin Najwa, 10, said her friend's giggles were replaced by screams as the bus "hit a bump" and lurched to the left.
Fatin "blacked out" and woke up to find herself buried in luggage.
"When I woke up I couldn't lift my head," she said. "Luckily my friend was around and she pushed a few bags away because I was stuck. Everybody panicked."
Nayli Ramlan, 12, said she clung to her unfastened seatbelt as the bus tipped.
"It was the scariest thing ever," she said. "I was playing on my friend's tablet and suddenly the teachers were screaming and suddenly the bus tipped over."
Nearby, a dozing Nur Amirah, 11, was awakened by a "loud bang". She said it felt like the steering wheel had come loose.
"My friends were screaming and shouting, just trying to get out," she said. "The bus tipped over to the left, I was sitting on the right but fell off my seat and ended up under the left seat."
The students injured in the bus smash were last night recovering at a Northbridge property owned by the Malaysian Government as police continued their inquiry into what caused the crash.
Four adults with the group remained in Royal Perth Hospital where they were all listed as stable. It is believed some had broken bones.
Paramedics raised the alarm about 7.40pm on Wednesday after spotting the damaged white Coaster as they rushed another man to hospital from a nearby crash.
Fire crews leaving the earlier crash near Noble Falls Tavern arrived quickly.
Major crash officers were last night interviewing the 51-year-old driver.
Det-Sen. Sgt Brian Hunter said investigators would determine if the Ballajura man was appropriately licensed to drive the 29-seater bus.
Alcohol has been ruled out as a factor but heavy fog and limited visibility may have played a part.
Millennium Kids chair- woman Rachel Cochrane said the students were participating in a River Park Forum organised by the Swan River Trust, which involved about 100 children.
They were on their way back to their campsite at Lake Leschenaultia when the driver lost control.
The group missed the second day of the forum yesterday and are expected to fly home on Sunday.