Speed 'a factor' in horror crash that killed five teens south-west of Sydney

Police said the Nissan Navara left the road and hit a tree in Buxton, about 40 kilometres north-west of Wollongong, about 7.50pm yesterday.

The passengers - three girls, two aged 14 and a 15-year-old, and two boys, aged 15 and 16, all died at the scene.

The driver, an 18-year-old man on his green P-plates, who escaped life-threatening injuries, was arrested and taken to Liverpool Hospital for mandatory testing.

He remains in hospital this morning, receiving treatment for non-life-threatening injuries.

He has not been charged, and will be interviewed when it is "practical".

NSW Police Detective Acting Inspector Jason Hogan said the driver had returned a negative alcohol breath-test at the scene, but results for his mandatory tests were still incoming.

The six people had been in a car that was registered as a four-seater, Hogan said.

He said preliminary investigations suggested speed had been "a factor" in the crash.

Hogan said some of the next of kin had been drawn to the crash site along with first responders, alerted by social media.

Police are offering the families support.

Blaise Cox, a friend of one of the victims, visited the site of the crash this morning with her family.

"I'm feeling a bit shocked and still finding it hard to believe it," she said.

"She was my best friend and she was like an older sister to me."

A nurse living nearby heard the bang and rushed to the scene in her own car, performing CPR on one of the victims.

Witness David Pace said he was watching television at home when the crash happened right in his driveway.

Pace said he had heard a "loud bang".

"Came outside, I seen the tub of a car on my driveway, and looked to my right and there was the remainder of the car," he said.

"And, yeah, seen five dead bodies in it."

All five victims had attended Picton High School.

Some of them had been in the same class since Year Seven.

"The Picton High School community is devastated by the death of five young people in a vehicle accident last night," a NSW Department of Education spokesperson said in a statement.

"Our thoughts and deepest condolences are with the families and friends of the young people who lost their lives.

"Counsellors and extra staff will be on site at school today to support students and staff.

"We will also be working with local primary schools and providing extra wellbeing support where needed."

Superintendent Paul Fuller said it was one of the worst accident scenes he'd seen in 38 years and some of the first responders were likely to have known the victims.

"It's a horrific accident scene and a traumatic event like this will have a devastating impact on the families, friends and the local community," he said, overnight. 

"We have spoken to the principal of the high school to facilitate some counselling at the school tomorrow when the students arrive.

"A tragedy of this magnitude, it's gonna have ripple effects through the – for their family, friends and for the local community."

Local councillor Michael Banasik said the crash was a "terrible tragedy" for the tight-knit town of 400-500 people.

"It's devastating for Buxton and the general community, you know, it's just horrible," he told 9news.com.au.

"Buxton's a great place, small, small town and yeah, this is a terrible tragedy, no matter where it's happened."

Banasik, who struggled to put the impact of the accident into words, said what little was known about the crash was enough to "make everybody sick in the stomach", adding that the families involved would be devastated.

A medical team was flown in by helicopter to treat the victims, firefighters said.