'Devastating': Three mates killed in shocking camping trip smash

One family member mourning a "free spirited" man with a "gentle heart" said the friends weren't speeding and were all wearing seatbelts.

Three young mates heading home from a weekend away camping have been killed in a car crash in Perth's south-east.

Kyle Retallack, Joshua Cox and Chloe Websdale were on their way home when their Nissan Patrol crashed into a tree on the Brookton Highway.

The crash happened at 3pm yesterday in Lesley, about 35 kilometres from the CBD.

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"What I can say, the scenes that the first responders had to respond to were things that they'll probably never forget in their careers," acting Commissioner Mike Peters said.

The family of Cox, 26, and his family told 9News he was "free spirited" and had a "gentle heart".

They said the friends weren't speeding and were all wearing seatbelts.

A friend of 27-year-old Retallack described him as "a genuinely lovely person, [who] wouldn't hurt a fly", adding "he was always smiling and happy".

Websdale, 23, played A-grade cricket for the Rockingham Hornets, which said "this is devastating for our club".

Police say it is too early to know what caused the crash but are investigating.

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The car was so badly damaged it took fire and emergency services more than three hours to get the bodies out of the wreckage.

Five people lost their lives on our roads in a matter of hours yesterday, and WA police said they didn't know what else to do.

On Friday night, Seb Foufas lost his life in Pinjar, a passenger in a ute that flipped on a dirt track.

Two teens died in a motorbike collision in Roebourne, and another motorbike rider, a 32-year-old, killed at Allanson east of Bunbury

"We are certainly out there, every single day patrolling the highways. Our regional officers are undertaking road policing activities all the time. And I don't know what else to do," Peters said.

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