Police responded to a three-vehicle collision in Mapleton Township on Friday morning.
The crash happened in the area of Perth County Road 131 and Side Road 6 around 11:30 a.m.
Two people were taken to hospital as a result of the crash.
One person, a 76-year-old woman, sustained life-threatening injuries, police said.
Involved were an 18 wheeler filled with compressed gas, a ten-ton flat bed truck which lost half its load, and a sports utility vehicle.
The SUV left the road and ended up on its roof, sustaining serious damage to its front end.
Crews vented the gas from the tractor trailer as a precaution.
A spokesperson with Ornge air ambulance said they were responding to a collision with possibly two patients trapped.
The air ambulance was called off before it arrived.
The road was closed for several hours while crews cleaned up.
