A truck breakdown on Great Eastern Highway eastbound is causing major congestion during peak-hour traffic on Thursday afternoon.

The breakdown is located before Coolgardie Avenue in Ascot and was reported by Main Roads at 3.54pm.

The left lane is completely blocked by the truck, causing heavy traffic leading up to the site.

Main Roads has urged drivers to exercise “extreme” caution and to allow for a safe merge if travelling in the area.

A crash on Great Eastern Highway northbound is also causing headaches for commuters travelling home.

The crash is located before Guildford Road in Guildford and was reported by Main Roads at 5.05pm.

The left lane has been partially blocked by the crash and there is debris scattered across all lanes.

Main Roads has reminded drivers to remain alert if in the area.