An investigation has been launched into how a man was killed by his own runaway truck.

The refrigerated truck crashed into the man on a northbound ramp from the Pacific Highway onto the Pacific Motorway in Wahroonga, north Sydney, about 4.25am on Thursday.

A man has died after being struck but his own truck on the Pacific Hwy.

 

Police believe the truck rolled onto the driver before a passerby was able to enter it and pull the emergency brake to stop it from entering traffic.

The man, who is yet to be formally identified, died at the scene despite the best efforts of paramedics.

A crime scene has been established as police determine the circumstances surrounding the death.

Transport for NSW has warned commuters to instead “use an alternative route (and) allow extra travel time” as the ramp remains closed into peak-hour traffic.