A man has died after allegedly driving the wrong way down the M1 motorway north of Sydney and crashing into an oncoming car.
Police say the 39-year-old died en route to Gosford Hospital in an ambulance after the crash in the northbound lane at Mooney Mooney near the Hawkesbury River Bridge about 8.30pm on Wednesday.
The driver of the other car, a 57-year-old woman from Kincumber, was flown to Royal North Shore Hospital in a critical condition after sustaining two broken legs and internal injuries.
Three passengers in her car, two men aged 26 and 32, and a 28-year-old woman, sustained serious but non-life threatening injuries and were taken to the same hospital by road ambulance.
Police will prepare a report for the coroner.
Karina Hogan said she saw the wreckage on her way home from work at 1am.
"They were shredded. Both cars were torn apart like they were made of paper. Truly horrible for all involved," she posted on Facebook.
Earlier on Wednesday a man died after a two-truck smash north of Sydney on the Thunderbolts Way near Gloucester.
The smash sent the two trucks into a retaining wall and through a guard rail before crashing down a steep embankment and coming to a stop about 50 metres down the hill.
The driver and sole occupant of one of the trucks, a 32-year-old Karuah man, died at the scene.
A 47-year-old man and 51-year-old woman in the second truck were flown to John Hunter Hospital for treatment of non-life threatening injuries.
AAP with Rachel Olding