A man has been charged over a fatal car crash that killed a 23-year-old pregnant woman and her unborn twins as well as a 17-year-old girl in Sydney's west.

Newlywed Katherine Hoang (nee Gordon) and 17-year-old driver Anh Hoang, who is also known as Belinda, were killed in the collision at Orchard Hills, near Penrith on Friday night.

Katherine's husband Bronko Hoang, 25, suffered a critical head injury and is in an induced coma at Westmead Hospital.

The high-impact crash left one driver trapped in the wreckage for a short time. ( ABC News )

The couple were married in May and were expecting twins, who were also killed in the accident.

All three were travelling northbound in a Nissan Tiida on the Northern Road when they were hit by a Mazda 3 travelling south.

The driver of the Mazda 3, 29-year-old Richard Moananu, has been charged with 10 offences, including two counts each of manslaughter and aggravated dangerous driving occasioning death, negligent driving and driving unlicensed.

Police allege Moananu was driving more than 45kph over the speed limit and on the wrong side of the road.

His matter was mentioned today at Parramatta Bail Court, where his lawyer did not apply for bail and bail was formally refused.

He remains in Westmead Hospital in a stable condition under police guard.

'A huge hole in my heart'

One of Bronko's friends, Nino Pace, took to Facebook to express his devastation at the accident.

He met Bronko through the events industry and the accident had "hit home very hard".

"To hear what has happened to him and his family on Friday night has placed a huge hole in my heart," he wrote.

"My prayers are with you brother; I hope you make it through and we share more memories together."

At the crash site on Saturday, local resident Mark and his two young daughters planted a small tree.

"Just planting it … every time I drive past I'm going to think of these people, and people in this area are going to think of these people," he said.

An Orchard Hills local resident planted a tree at the site of the car collision. ( ABC News: Jonathan Hair )

Mark said he did not know the victims but he and many locals had been deeply affected by the accident.

"I'm really touched, and I know a lot of people in the area … everyone's feeling this.

"It's just a catastrophe [for the family] and I'm really feeling it, and I'm hoping everyone gets together and does what they can to try and prevent this stuff from happening in the future."