M1 Southbound lanes reopen after metal shards cause traffic chaos for Sydney commuters

All southbound lanes of the M1 Pacific Motorway have reopened following a massive clean up of small metal shards which damaged hundreds of cars.

The motorway was closed for hours between Ourimbah and Mount White on the NSW Central Coast, after a truck lost its metal load early this morning.

Those motorists who drove through the area after five am before the road was closed are being urged to get their tyres checked, in case of undetected damage.

Authorities were forced to close the road about 5am after the truck lost the metal between Palmdale and the Mooney Mooney Bridge.

An almost 30-kilometre stretch of the motorway was closed between Ourimbah and the Calga Interchange.

Earlier today NSW Roads Minister Jenny Aitchison said it was a unique incident.

"This is an unprecedented situation," she said.

"We are working with all the resources of government and the private sector to do the clean up.

The minister said the priority is clearing a backlog of B-double trucks unable to turn around.

"That will ease the congestion," she said.

"We are looking at a very protracted situation, we're talking hours and potentially to the end of day."

NSW Police confirmed they received reports that more than 300 vehicles had been damaged by the metal shards. 

Police and the Transport Management Centre (TMC) are launched a significant operation to clear the motorway.

TMC coordinator Howard Collins said there were currently "traffic tailbacks" stretching for up to 40 kilometres.

He said the truck was carrying more than 700 kilograms of scrap metal.

"The backdoor of that vehicle has come open and spread thousands of pieces of sharp metal all across the motorway," he said.

"Hundreds of vehicles have had their tyres punctured by this metal.

"I've seen photographs [of] multiple tyres, so it's no use changing one tyre, because three or four have gone."

Insurance to pay

Trucking company NJ Ashton from Horsley Park in Sydney's west said one of its trucks was responsible for the spill.

Company spokesperson Daniel Falconer said the driver set off south towards Sydney this morning with 40 tonnes of scrap metal on the back, with some of the material spilling from the back.

He said the driver, who had been doing the journey for the past three months, loaded the truck yesterday afternoon and there were no signs of a problem. 

"He didn't see it, he didn't know … We don't know exactly how it's been done, a mechanical error of some sort," Mr Falconer said.

"Definitely our problem, we take full responsibility.

"'If anyone needs any assistance, we'll be paying for everything through our insurance."

NSW Police said a 46-year-old male truck driver was assisting officers.

Mr Collins said the company would also assist with the clean-up.

"The boss, apparently, is sending sweepers, a sort of magnetic device which picks up the metal, because it's going to take us hours to do this," he said.

"It really is a difficult job, never seen it before, hopefully never again."

Emergency services will assist the TMC with removing cars from the motorway. 

'Cars are scattered'

Motorist Jon Heaney described the situation as "pandemonium".

"Cars are scattered, they're all on the verge ... some are in the slow lane," he said.

Another motorist told the ABC a warning about the incident came too late for scores of drivers who ran over the metal in foggy conditions.