A truck has rolled and caught alight north of Sydney this morning, leaving a man dead and causing major delays between Sydney and the Central Coast.

Key points: The body of a man, believed to be the driver, was found at the scene

The body of a man, believed to be the driver, was found at the scene Drivers are being warned of major delays and are advised to take the train if possible

Drivers are being warned of major delays and are advised to take the train if possible The truck was driving on the M1 at Mount Kuring Gai when it crashed into the median strip

The truck was driving on the M1 Pacific Motorway at Mount Kuring Gai when it crashed into the median strip and rolled before catching fire.

Emergency services were called to the southbound lane about 2:30am on Tuesday and discovered the body of the man.

NSW Police said the man was believed to be the driver but the body was yet to be identified.

Officers from Kuring Gai Police Area Command have established a crime scene and an investigation is underway.

Emergency services called to the southbound lane of the M1 found the truck, carrying wool, in flames. ( ABC News )

There are major delays in the area, with traffic on the M1 queued for about 8 kilometres, while traffic on the Pacific Highway, where motorists are being diverted, is queued for around 17km.

The Transport Management Centre said due to the serious nature of the crash, there was no forecast for when the motorway would reopen.

Southbound motorists are being diverted on to the Pacific Highway at Berowra.

Northbound motorists can no longer access the M1 from the Pacific Highway or Pennant Hills Road at Wahroonga.

The Transport Management Centre said people travelling between Sydney and the Central Coast should delay their journey, allow plenty of extra travel time due to increased volumes on the Pacific Highway or consider catching a train instead.

The B-double truck was carrying wool which was destroyed in the blaze.