Man dies trying to cross major Sydney road

A 71-year-old man has died after he was hit by a car while trying to cross a motorway in Sydney's northwest.

The man was walking over the M2 at Baulkham Hills about 10.50am on Saturday but was struck by an oncoming vehicle, near the Windsor Road off ramp, police said.

NSW Police and four NSW Ambulance crews raced to the scene, and a CareFlight helicopter was also called.

The critically-injured pedestrian was transported to Westmead Hospital but he died en route.

Police say the male driver, believed to be in his mid-twenties, stopped after the incident and was taken to hospital for follow-up medical tests and checks.

The crash forced the temporary closure of the motorway's two citybound lanes.