WA driver dies after trailer disconnects

A man has died after a trailer carrying quad bikes disconnected from another vehicle and hit his truck south of Perth.

The 55-year-old man was driving on the Brookton Highway in Kelmscott on Friday when a trailer carrying quad bikes hit his vehicle.

The trailer had been hitched to a caravan being towed by a ute when it disconnected and crossed to the other side of the road, police say.