Dramatic footage has emerged of a woman walking across traffic lanes in Northbridge tunnel

Shocking footage has emerged of a woman stumbling across lanes of a busy Perth tunnel in a potentially life-threatening stunt.

The vision shows the woman confronting cars hurtling through the Northbridge tunnel eastbound on the Graham Farmer Freeway about 5am on Saturday.

She was holding both of her arms up in the air and walking forwards and backwards along the fast lane of the tunnel.

Motorists were forced to slow from 80km/h and drive around her at one point as she stepped into the middle lane, and waved what appeared to be a sweater in the air.

The 1.6km tunnel, opened in 2000, is a vital link connecting the Mitchell Freeway and western Perth suburbs with Belmont and other eastern suburbs.

But walking and cycling on the freeway is illegal, with motorists only advised to change lanes if necessary.

At the Main Roads tunnel operations centre in Northbridge, operators monitor the tunnel 24 hours a day via CCTV.

WA Police has been contacted for comment.