A major highway has been closed for hours as police investigate the death of a man found unresponsive on the road.

The man aged in his 40s was discovered on Tonkin Hwy in Noranda, in Perth’s northeast, at just before 2.30am on Thursday.

WATCH THE VIDEO ABOVE: Man found dead on Tonkin Highway in Perth.

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Police and St John WA paramedics raced to the scene, just north of Benara Rd, but the man had suffered serious injuries and could not be saved.

Major Crash detectives have spent the majority of Wednesday looking into how the man was injured and ended up on the road, and provided an update just after 3.30pm.

“It is believed the deceased man was struck by a vehicle that left the scene,” police said.

“A woman is currently assisting police with their inquiries.”

A northbound stretch of Tonkin Hwy between Morley Dr and Reid Hwy is due to be reopened at about 4pm, after being closed all day.

The shutdown caused headaches for morning drivers, with traffic diverted away from the area.

Even in the afternoon, authorities said congestion remains heavy and the advice remains to seek an alternate route.

Anyone with information into the incident or dashcam should contact Crime Stoppers.