One person unaccounted for, significant traffic delays as M1 closed after truck bursts into flames

A person is still missing after a tanker, reportedly carrying ethanol, burst into flames on the M1 Motorway near Lake Macquarie in NSW while motorists are being warned of significant delays.

Emergency services were called to the motorway near Cooranbong, about 1km south of the Freemans Drive interchange, at 12.50pm on Monday after reports two trucks collided and one had caught fire. A car was also damaged and another truck was involved.

NSW Police said one person remains unaccounted for after the crash.

"Police remain at the scene and crash investigators will examine all the circumstances surrounding the crash," the statement said.

"Police are yet to determine the exact circumstances of the incident and will provide more updates as they come to hand," a statement said.

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Police believe one truck was stationary while another one clipped it.

The truck fire also sparked a bush fire north of the crash scene which NSW Rural Fire Service officers are still fighting.

Motorists are advised to delay their travel or avoid the area if possible. Diversions are in place but there are expected to be significant delays.

Live Traffic NSW says Southbound traffic was backed up for about 11km at 3pm and motorists were advised to allow an extra one and a half hours travel time.

Northbound traffic was backed up for approximately 9.5km and motorists were advised to allow just over two hours of extra travel time.

Diversions are in place. Northbound traffic are diverting via Mandalong Road exit to Morisset to Wangi Road to Dora Creek and Toronto.

Southbound traffic can divert via Palmers Road exit and then Cessnock Road to Morisset to head southbound and rejoin the M1 Pacific Motorway.