Earlier: HEAVY traffic and significant delays are in place for northbound traffic on the M1 Motorway after a truck crash on Tuesday.

Two of three northbound lanes remained closed shortly before 10am after the collision, which Live Traffic NSW reported had begun hindering passing motorists about 7am.

Five NSW Ambulance crews were sent to the scene.

Paramedics treated three people - one was taken to Gosford Hospital in a serious condition with abdomen and chest injuries and another was taken to the same hospital with minor injuries.

Drivers are urged to allow extra travel time, exercise caution and reduce speed.

Salvage operations for the heavy vehicles involved are underway, with motorists warned intermittent closures could continue until the area is clear.

Diversions for northbound drivers include a route from the Kariong Exit along the Central Coast Hwy, Manns Rd, Pacific Hwy to re-join the M1 Pacific Mtwy at Ourimbah.

No details on injuries were immediately available.

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