Mark Porter and David Clark were airlifted to hospital after being pulled unconscious from their cars following their 180kph crash in the second tier Fujitsu V8 Supercar series race.

Crowds cried "no, no get up" as paramedics performed CPR on Porter after taking at least 10 minutes to cut him free through the passenger's door of his Holden Commodore.

The 31-year-old New Zealand-born father of one was immediately taken by ambulance to Bathurst Base Hospital where he was stabilised before being flown by helicopter to Royal Prince Alfred Hospital in Sydney in a critical condition.

It is believed both drivers have serious head and chest injuries, although Clark is thought to be in better condition than Porter.

After Clark was taken from his Ford Falcon on a sled stretcher and brought down from the mountain by ambulance, he was loaded onto the NRMA Careflight helicopter behind a white sheet.

The 26-year-old father of three from Adelaide finally took off for Nepean Hospital in Penrith also in a critical condition an hour after he ploughed into Porter's stalled car on a blind portion of the climb up the mountain.

His father Ken was in the pits as the manager of Clark's Optima Sports team and went with him to Nepean Hospital.

Clark's wife Leah flew from Adelaide to be at her husband's bedside.

V8 Supercars officials would not speculate on the cause of the crash in which Porter's MSport Racing Commodore suddenly spun sideways, stalled and left him stranded as a sitting target in the middle of the track.

As Gold Coast-based Porter climbed the mountain near Reid Park on the 12th lap of the 14 lap race, he spun and stalled and was clipped from the rear by Chris Alajajian who was unhurt.

Clark then came flying up the hill oblivious to what was ahead and sent his Falcon sideways in a desperate attempt to escape collision but crashed directly into Porter's driver's side door at around 180kph.

Emergency crews needed cutting equipment to get both drivers out of their battered cars as the crowds in Reid Park looked on in horror.

In the week in which motorsport prepares to honour the late Peter Brock who died in a rally crash last month, defending Bathurst 1000 champion Mark Skaife said the accident was another reminder of the dangers all race drivers face.

"We always go in there understanding motor racing is dangerous and we understand the risks," Skaife said.

"V8 Supercars are, by world standards, incredibly safe and this circuit over a long period of time had spent huge amounts of money on safety.

"I think Bathurst is as safe as any big fast circuit. "We wish those guys well and their families too, there was a lot of concern up and down pit lane."

Amid speculation on the cause of the crash, one driver said he noticed Porter's car had been dripping oil, which his rear tyres may have caught and caused his sudden spin.

Ford driver Jason Bright, who qualified second fastest for Sunday's Bathurst 1000, said he hoped drivers would learn from the accident.

"You learn from every incident you see," he said.

V8 Supercars chairman Tony Cochrane said the accident reiterated the dangers of the sport.

"It's a terrible accident and our thoughts are with the families and we just hope for a good outcome," Cochrane said.

"We just have to wait and see."

Confederation of Australian Motorsport (CAMS) president Colin Osborne said CAMS and V8 Supercars Australia have initiated support services for the families of both drivers.

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