Grave fears are held for critically injured New Zealand race car driver Mark Porter who was late last night fighting for his life in a Sydney hospital after a horror smash at Bathurst.

Porter's Kiwi wife Adrienne and his parents, Robyn and Robin, were at his bedside in the Royal Prince Alfred hospital with many friends and supporters keeping vigil outside.

Hamilton-born Porter, 31, was airlifted to hospital in a critical condition after fellow V8 driver David Clark ploughed into his stalled Holden Commodore at close to 180km/h during a second tier V8 race at the Bathurst 1000 meeting.

The accident came exactly four weeks after the death of Peter Brock.

It took at least 10 minutes to cut Porter free through the passenger's door of his Holden Commodore. Porter has a serious head injury as well as extensive internal fractures and abdominal injuries. Reports last night said he was only being kept alive by life support.

"Mark is still critically ill and still fighting his horrendous injuries," said Robin Porter who arrived with his wife yesterday morning from Hamilton to be with their son.

Mark's wife Adrienne, with whom he has a 1-year-old son Flynn, flew to his bedside from their Gold Coast home on a plane organised by five-times world 500cc motorcycle champion Mick Doohan.

Clark, 26, regained consciousness overnight in Nepean Hospital in Penrith and was in a critical but stable condition in the intensive care unit. Although not yet talking, he has shown signs of mental alertness. He has been treated for a collapsed lung and fractures to his pelvis, right arm and knee cap.

Phil Curtis who works as an engineer for Porter's Msport Racing team, yesterday gathered with family and friends at the hospital to support "a good bloke and mate".

"Everything is still the same. He's holding on. That's the main thing," Curtis said.

"He's a fighter. We hope he can get through this."

Curtis said Porter's parents and wife were "as good as they can be under the circumstances".

"They are trying to stay positive. You have to in this type of situation," he said.

"There's always risk with motorsport, but this sort of thing normally doesn't happen. It is pretty hard for everyone to take."

Another member of the team, Doug Rohl, said while things appeared grim, everyone was hoping for the best.

"It's not an easy time for any of us," Rohl said. "We just hope he comes through this."

The car Porter was driving suddenly spun sideways on a climb up the mountain on the 12th lap of the 14 lap race, stalled and was left stranded in the middle of the track in an area blind to oncoming traffic. Clark sent his Falcon sideways in an attempt to escape collision but crashed directly into Porter's driver's side door.

Porter, who celebrated his 31st birthday on Monday, had been a front-runner in the second-level series for several years. Porter, who set up the Msport Racing team in Queensland, had a busy year behind the wheel and was sitting in third position 2006 V8 Development Series.

V8 Supercars chief executive Wayne Cattach said a thorough investigation would be held into the crash.

"It would be premature of me to speculate what the implications are but there will be a very close and intensive look at it."

Porter was scheduled to drive the second BOC Gases Ford in the Bathurst 1000 tomorrow with Dale Brede and has been replaced by Michael Caruso. Brede told the Canberra Times yesterday he questioned his own mortality after the crash.

"I suppose what it does, it hits home with the Brocky situation," he said. "You just realise... you're not invincible. You can go from just walking around to being in hospital in a coma with massive injuries, grasping for your life."

Three men have died driving at Bathurst - Mike Burgmann in 1986, the 1967 Formula One world champion Denny Hulme suffered a fatal heart attack while driving in 1992 and Don Watson in 1994.

By Stephen Cook Email Stephen, Agencies