Update, 1.30pm: Five young children are among 10 people who have been airlifted to hospital after a horror crash near Southern Cross last night that killed three men.
A Royal Flying Doctor Service spokeswoman said four planes were required to transport the patients, who were all in a serious condition, in the biggest emergency she had seen in her time working at the service.
A man and a woman aged in their 60s, two women aged in their 30s and a 25-year-old man were all flown to Royal Perth Hospital.
Three girls aged four months, one-year-old and three and two boys aged three and four were flown to Princess Margaret Hospital.
The crash happened at 7.40pm, about 10km east of Southern Cross on Great Eastern Highway.
The 23-year-old driver of the sedan, 20-year-old sedan passenger and 38-year-old van driver were killed in the crash.
The van is understood to have been carrying five adults and five children.
Major crash investigator Det Sen Sgt Garry Nicolau said the Ford sedan was travelling west on Great Eastern Highway and when the driver tried to overtake a large truck and collided head on with the Toyota van.
“It appears the driver of the Falcon was overtaking when it was quite clearly unsafe to do so,” he said.
It is understood the three men in the Ford sedan were friends living in Kalgoorlie while the people in the Toyota van were two related families from New South Wales.
The two youngest children suffered severe head injuries in the crash and are in a critical but stable condition in hospital today.
The remaining injured people are all in a serious but stable condition.
It is understood police commissioner Karl O’Callaghan was due to travel to Kalgoorlie today and planned to stop at the scene of the crash.
A St John Ambulance spokeswoman said four ambulances and a community paramedic were called to the crash and transported the injured to Southern Cross before they could be airlifted to Perth.
She said the three men at the scene.
A RPH spokesman said the five adults transported to the hospital were all in a serious but stable condition this morning.
Great Eastern Highway is expected to remain closed until midday today and a detour is in place via Emu Fence Road and Marvel Loch Road.
The RFDS spokesman said RPH doctors were last night able to communicate with RFDS doctors through a video conferencing link to help guide immediate triage and treatment of the injured.
"It's been a huge collaborative effort," he said.
The first of the four RFDS planes landed in Perth at 1am this morning and the last landed at 4am.
Det Sen Sgt Nicolau said the consequences of the crash were “absolutely devastating”, not only for the families who had lost loved ones but also for police officers and emergency services.
He urged motorists travelling long distances on country roads to drive safely, particularly as there was increased traffic on the roads because of schools holidays.
“Take regular breaks, don’t drive tired,” Det Sen Sgt Nicolau said.
“If you are going to overtake a vehicle, make sure that the road is clear, if the road is not clear do not overtake.
“That one or two minutes extra that it takes for you to wait for that road to be clear could mean that you may save your life or you may save others lives.”
Det Sen Sgt Nicolau said investigators would be relying heavily on witness accounts because both drivers had died.
He said everyone in both cars was properly restrained at the time of the crash.
A police plane has flown four major crash investigators from Perth to the scene and forensic officers are expected to arrive this morning.
A police spokesman said officers were investigating whether speed or alcohol were a factor in the crash.
The deaths bring the road toll to 137 this year, including 73 on country roads.