A truck accident brought the Mitchell Freeway to a standstill on Tuesday morning, with early reports suggesting traffic has become backed up to Powis Street.
The accident occurred southbound on the Mitchell Freeway at around 9.55am during the tail-end of Perth's peak hour traffic, when a truck collided with the Hay Street overpass.
Main Roads WA spokeswoman Bernie Dimanlig said the truck had since left the site, and emergency services were doing their best to manage oncoming traffic.
"Our main concern is managing the traffic at the moment, and the two centre lanes are now blocked by police," she said.
"At the moment there is a lot of debris on the road... police are cleaning up what they can and a pick-up truck is now on site helping remove some of the larger boulders."
Main Roads WA were unable to confirm how badly Hay Street overpass was damaged during the accident, but said bridge management services would attend the scene later in the morning to assess the damage.
Main Roads WA traffic management are on route to the accident.
The right lane remains blocked.