A crash in the Northbridge tunnel has slowed footy fans trying to reach Optus Stadium for the western derby.

Main Roads WA said a single left lane of the tunnel, eastbound, is closed after a collision about 4pm on Friday. Drivers are urged to approach with caution.

Police and tow trucks are at the scene, on the Graham Farmer Freeway, as thousands passed by trying to reach Optus Stadium early.

A video posted by Main Roads WA showed traffic slowly passing two cars involved in the crash, which is not believed to be serious.

Main Roads previously warned punters to allow extra travel time ahead of the western derby clash between West Coast and Fremantle.

Gates at Optus opened at 4.30pm — in the middle of peak hour traffic — before the match starts at 6.10pm.

“Expect extra congestion on Graham Farmer Freeway, the tunnel eastbound, CBD and around the Stadium from 4pm Consider taking public transport,” they said on X.