Clean-up under way after debris damages hundreds of cars on M1 motorway north of Sydney

The clean-up is under way after hundreds of vehicles suffered tyre damage when a truck spilled metal debris on one of Australia's busiest highways.

All southbound lanes of the M1 motorway north of Sydney have now been reopened from Ourimbah to Mount White, a 30km stretch of road.

Drivers have been advised to allow extra time for travel in the area, with heavy delays on the Old Pacific Highway and Peats Ridge Road.

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The NRMA responded to the dozens of cars that remain beside the roadside, with drivers needing to change their tyres.

NRMA roadside assist vans and tow trucks have been deployed to both ends of the incident.

They are working to tow vehicles out of the closed section of the highway.

It is "probably one of the biggest incidents we've responded to over the years", a spokesperson for the company said.

Chief Inspector Thomas Barnes of NSW Police's Highway Command told 2GB the debacle is "somewhat unprecedented".

"A number of people are not realising until they've arrived at their destination that they've also got damaged tyres that are subject to a slow leak," Barnes said.

He said anyone who had driven down the M1 should inspect their tyres because of the possibility of a slow leak.

Trucking company sorry

The owner of the trucking company has apologised for the debacle.

NJ Ashton general manager Daniel Falconer said he wasn't 100 per cent sure how it happened.

"We've been doing this for about three or four years and we've never had a problem," he told 2GB.

"The tins on the back of the truck were locked. We don't know how it has come out of the back of a truck."

Falconer said the driver had "absolutely no idea" the steel fragments were coming out the back of the truck.

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Ashton said the driver was "devastated" by what happened.

"We're very, very sorry for what's happened," he said.

"We're doing as much as we possibly can."

B-doubles are being parked on the roadside and motorists have been urged to allow for extra travel time.

Anyone who has suffered damage as a result should contact NJ Ashton, with the company's insurance to cover the costs.

Traffic is now being directed to the Old Pacific Highway, but that road is gridlocked with so many cars now on it.

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