A van crashed and rolled onto its side in Greystanes on Wednesday evening.
Police said the vehicle was travelling on the Great Western Highway, about 100 metres east of Beresford Road, just before midnight.
The van then struck a power pole and rolled onto its side, trapping the driver inside.
Emergency services arrived and freed the driver, a 37-year-old man, from the vehicle and treated him at the scene.
There were no passengers and no one else was reported to be injured.
The driver had sustained multiple injuries and was taken to Westmead Hospital in a critical condition.
The Great Western Highway was closed for about one hour.
Investigations are continuing.