Mr Proctor was cut out of his car and taken to Liverpool Hospital, where he remained on Saturday in a critical condition.
The 65-year-old female driver of the Honda Civic was taken to the same hospital, where she also remained in a critical condition on Saturday.
Two teenagers in the Triton and the driver of the Yaris were not injured.
Vision of the crash, broadcast by Nine News on Friday, shows the Civic travelling in the left-hand lane before it drifts across the middle lane and hits the officer’s oncoming hatchback.
Van driver Kamran Rowshanzadeh, whose dash cam recorded the crash, said he initially thought the car was trying to cut into his lane without using its indicator.
“Next thing I know it was actually drifting,” he said.
He was able to swerve around the cars as they impacted in the single northbound lane.
“The car literally came off the ground and the back kicked up and I dodged it. It was just so sudden and so quick,” Mr Rowshanzadeh said.
He added that he heard the officer brake at the last second.
“I hope everyone’s okay and my heart goes out to their families,” he said.
Mr Proctor graduated from the NSW Police academy in April 2018, as part of class 333, and was one of 15 officers posted to the Liverpool region.
Speaking to the Liverpool City Champion shortly after his graduation, Mr Proctor said he was formerly a volunteer firefighter and had worked in IT repairing laptops before deciding to pursue a career in policing.
He said he had grown up in the area and noticed a “bad perception” of police, which he wanted to change.
Speaking to reporters, Acting Inspector Melissa Thompson from NSW Police said the accident was “devastating” and said it was “extremely upsetting” for police to arrive and find one of their colleagues injured.
Heathcote Road was closed for six hours on Thursday while officers from the Crash Investigation Unit examined the scene.
They continue to investigate the incident.
Georgina Mitchell is a court reporter for The Sydney Morning Herald.