A breakdown on Mitchell Freeway southbound in the Perth CBD is causing peak hour mayhem for commuters heading home on Thursday evening.

The breakdown was reported at 5.38pm and occurred on the busy stretch of Freeway after Mounts Bay Road, before the Narrows Bridge.

The right lane has been blocked by the breakdown and traffic is slow leading up to the site.

Main Roads has reminded motorists to drive with caution if travelling in the area.

Earlier, a crash on Kwinana Freeway southbound caused early peak hour mayhem near the Mount Henry Bridge.

The crash occurred on a busy stretch of Kwinana Freeway in Salter Point just before Mount Henry Bridge and was reported by Main Roads at 3.55pm.

The left lane was blocked by the crash, which caused heavy congestion during peak hour.

The crash has since been cleared, but traffic remains slow on approach.

Further east, a truck breakdown is also wreaking havoc for motorists travelling along Tonkin Highway northbound in Wattle Grove.

The breakdown was reported by Main Roads at 3.16pm and has blocked the left lane.

Traffic is slow in the lead up to the site, and Main Roads has urged motorists to allow for a safe merge.