Three girls, two aged 14 and one 15, and two boys, 15 and 16, died in the single-vehicle crash on Tuesday night.
The Picton High School teens were passengers in a Nissan ute being driven by an 18-year-old man when it left the road and struck a tree near the Wollondilly Shire village of Buxton about 8pm.
The ute was torn apart and all five died at the scene.
The driver survived, was arrested and taken to Liverpool Hospital with non-life threatening injuries to undergo mandatory blood and urine tests.
Camden police chief Superintendent Paul Fuller who has been in the force for 38 years said "It's one of the worst accident scenes I have ever come across".
At least three of the victims were in year 9 and distraught teenagers wearing their school uniform laid flowers and cards on Wednesday at the site where their mates met their fate.
A Facebook post by Picton High School said it was "prioritising support for our students as they come to terms with this terrible news", with extra counselling in place.
The Education Department said the school community was devastated and offered "deepest condolences" to "the families and friends of the young people who lost their lives".
Premier Dominic Perrottet also offered condolences, saying "our hearts go out to them at this difficult time".
Supt Fuller said some of the victims' parents rushed to the scene shortly after the crash.
"We had parents turning up ... who had found out through social media that their kids may have been involved in this crash," he told Sydney radio 2GB.
A police family liaison officer worked with the families to identify the children.
The P-plate driver remains in hospital with minor injuries and police hope to speak to him later on Wednesday.
Alcohol is not thought to be a factor in the crash.
Supt Fuller said police would be investigating how six people came to be travelling in the ute, which was designed to carry four, and urged parents to know where their children were.
"Know who your kids are getting into a vehicle with, who that driver ... is and can they be trusted," he said.
Footage of the mangled wreck showed the ute shredded, with debris strewn for metres.
NSW Fire and Rescue Superintendent Adam Dewberry said some of the first responders at the scene knew the victims and were being counselled.
"Our firefighters live in the community they're responding to," he told ABC TV.
"We're conscious of that and we'll be providing all the support we can."
Wollondilly Shire Mayor Matt Gould said the Buxton community was waking up in shock and mourning.
"The loss of so many young lives is just devastating and you can't put into words the overwhelming loss many in our community are feeling," he posted on Facebook.
"Our thoughts are with the Picton High and Buxton communities and particularly with the family and friends of those involved, as well as the emergency responders who had to deal with such a heartbreaking scene.
"There's an awful lot of people in the shire that are hurting today, so we need to be there to support and look out for each other."
Investigators are appealing for anyone with dashcam footage or information to contact them.
10°C