Perth motorists endured a nightmare commute as crashes, a bus breakdown and blacked-out traffic lights triggered widespread delays across the city on Friday morning.

The biggest headaches hit the northbound Kwinana Freeway before Rowley Road at Mandogalup, where a crash caused major congestion during peak hour.

While the crash has since been cleared, traffic remains heavy on approach, with an emergency lane briefly closed as towing crews worked at the scene.

Further chaos unfolded in Welshpool after a bus broke down on Orrong Road eastbound at Bell Street.

Incident Response crews shut the left lane while traffic crawled through the area, with motorists warned to exercise caution approaching the breakdown.

Earlier, blacked-out traffic lights at the intersection of Hale Road and Welshpool Road East in Wattle Grove added to the frustration.

The signals have since been restored after drivers were forced to slow down and treat the intersection under give-way rules during the morning rush.

Another crash near Gnangara Road and Alexander Drive at Cullacabardee also caused lingering delays across Perth’s northern suburbs.