The man accused of causing the death of two women in a car crash, one of whom was pregnant, could potentially face charges over the death of her unborn twins.

Richard Moananu, 29, has been charged with two counts of manslaughter after the car he was driving collided with a Nissan driven by a 17-year-old learner driver on the Northern Road at Orchard Hills at 7.45pm Friday night.

The teenager and a heavily pregnant Katherine Hoang, 23, died at the scene.

Ms Hoang, who was due to give birth in weeks, was seated in the backseat of the Nissan.

Bronco Hoang (right) remains in an induced coma in hospital. (Facebook)

Richard Moananu, 29, remains in hospital in a critical condition under police guard. (9NEWS)

Her husband Bronco, 25, was the front passenger in the car and was taken to Westmead Hospital in a critical condition.

The tragedy has struck a chord with young mum Brodie Donegan, who lost her unborn daughter Zoe in a crash in 2009.

“I just felt so sorry. It’s such a loss felt by everyone,” Ms Donegan told 9NEWS.

Brodie Donegan wants unborn children to be recognised as human lives in car crashes after she lost her own unborn daughter in a car crash. (9news)

The cars collided on the Northern Road in Orchard Hills on Friday night. (Nine)

Ms Donegan has spent years campaigning for fetuses to be recognised as human lives in the event of a car crash, with proposed legislation dubbed Zoe's Law.

“When you can feel the children, you’re looking forward to that birth, you are looking forward to that child,” she said.

Under current law, the death of an unborn baby is only recognised as serious injury to the mother.

The state government has no plans to change the law despite many believing an unborn child should be treated as a living person.

Mr Moananu is already facing 10 charges including two counts of manslaughter and police are making enquiries on if the 29-year-old can be charged over the death of Ms Hoang's unborn twins.

“My daughter was my daughter. Katherine’s sons were her sons. They were also going to be imminently born,” Ms Donegan said.

Family members remain at Bronco Hoang's bedside today as he remains in a coma fighting for life.

Along with the manslaughter charges, Mr Moananu has been charged with a string of other offences including aggravated dangerous driving occasioning grievous bodily harm.

Katherine Hoang - who was heavily pregnant - was killed along with her unborn twin babies (Facebook)

Court documents allege Mr Moananu was on the wrong side of the road. (Nine)

He has also been charged with two counts of aggravated dangerous driving occasioning death, cause bodily harm by misconduct, driving unlicensed and two counts of negligent driving occasioning death.

He remains under place guard in Westmead Hospital, where he is in a stable condition.

Court documents allege Mr Moananu does not hold a licence, was on the wrong side of the Northern Road at the time of the collision, and was more than 45km/h above the speed limit.

Mr Moananu was trapped in his car following the crash and, after being cut from the vehicle, was transported to Westmead Hospital in a critical condition, where he remains under police guard.

The impact of the crash was so forceful that both cars were crushed beyond recognition into cubes of mangled steel and shattered glass.

NSW Ambulance acting inspector Joe Ibrahaim told 9NEWS he has never seen a crash scene like it.

"This is probably one of the worst scenes I have been to in my career," he said.

"One (man) has limb injuries, a pelvic injury and a head injury, the other one also has a head injury and has been put into an induced coma by our medical team."

Witness Jarrad Sherlock was one of the first people on the scene and immediately offered assistance to the Hoang family.

"The crash was so bad, I was just looking - I literally had to look for people in the car," he told 9NEWS.

"I was just telling (the driver) everything was going to be okay, trying to reassure her.

"I don't even know if she could hear me, because she was dropping in and out of consciousness."

Two other vehicles were also hit in the collision but none of their occupants were injured.