SYDNEY - A truck spilled 750 kg (1,653 lb) of sharp metal debris across one of Australia’s busiest highways on Friday morning, authorities said, forcing city-bound lanes to close, damaging hundreds of vehicles and sparking traffic chaos.

New South Wales state police said the incident occurred on the M1 Pacific Motorway in the early hours of the morning, leaving over 300 vehicles with tyre damage.

The M1, a freight and commuter route that runs north of Sydney, remains partially shut as emergency services clear the debris, using magnets and working to "hoover up the highway".

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State Highway Patrol Commander Howard Collins said it would be “more than several hours” until the motorway could reopen.

“It's not just a case of getting a road sweeper out or guys and girls with brooms. We are using some magnetic devices. We are removing embedded metal in the highway itself. This takes a long time,” he told a press conference.

Collins said the truck had travelled over 30 km (18.64 miles) before the spillage was detected.

“Around about 300 vehicles have been impacted - maybe more - by what now we know is over 700, maybe even 750 kg of metal debris from the back of a truck, which spread this metal debris for over 30 km," he said.

State Roads Minister Jenny Aitchison said the situation was “unprecedented”.

“We are working with all of the resources of government and the private sector to do the clean-up," she said.

"If you imagine it's like trying to hoover up the highway. It's very difficult."

The truck driver, a 46-year-old man, was cooperating with inquiries, police said.

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NJ Ashton, the haulage company that owned the truck involved, apologized for the accident and said it was helping with clean-up efforts.

“We’re taking full responsibility for what’s happened and are very sorry for any damage and disruption that’s been caused,” it said in a statement on its website.

“We still don’t fully understand how this occurred.”