UPDATE: A woman and her two young sons were killed in a crash near Gidgegannup this morning.
The 28-year-old woman and her sons, aged three and six, all died at the scene of the crash, police said.
It is understood a truck and a four-wheel-drive vehicle collided on Toodyay Road about 8.55am.
Emergency services and firefighters from Ellenbrook, Midland, Mundaring and Wundowie were at the scene near Noble Falls Tavern about 40km east of Perth.
There have been unconfirmed reports that one of the vehicles exploded on impact.
The three fatalities were from the 4WD. There were no other injuries.
Police say initial information suggested a fourth person had serious injuries but this was incorrect.
Noble Falls Tavern owner Brian Wickins said the crash had just happened when he arrived at his business on Toodyay Road today.
Mr Wickins said a staff member who witnessed the crash had alerted emergency services.
“It just shakes you right up just to see that,” he said.
The staff member reported an explosion after the crash but no fire.
Mr Wickens said he believed the 90km/h speed limit on the road was “too fast” on a dip in the road near the crash site.
He said trucks often travelled at high speed on the road and his customers regularly complained about being unable to turn into his business as a result.
“Perhaps it’s time for Main Roads to look at getting the speed limit dropped,” he said.
Main Roads has been contacted for comment.