Police have confirmed that the mother was allegedly behind a stabbing attack on three young children that left one dead and two others fighting for their lives in hospital.

The woman, aged in her 40s, is also in a critical condition.

A group of cyclists found a mother in her 40s and three young children with stab wounds on Waratah Road, Valley Heights, near Springwood, early on Sunday afternoon.

One young child died at the scene despite witnesses rushing to help, providing first aid while waiting for emergency services to arrive.

The children were found in a car that had partially pulled into a vacant block near a fire trail leading into the national park, with the woman found nearby outside the vehicle.

Waratah Road resident Peita Davies said residents on the street all knew each other and did not believe the woman or children were from the area.

‘Nobody heard anything,’ she told the Sydney Morning Herald. ‘We all want to know how they ended up here.’

Local Glenn Lyall said he initially mistook the heavy police presence for the aftermath of a car crash.

Police have confirmed that the mother was allegedly behind a stabbing attack on three young children that left one dead and two others fighting for their lives in hospital. 

The alleged domestic violence incidence in the Blue Mountains came at the end of a violent weekend

‘I could see a hatchback on an angle and two cyclists pointing, and I thought the car had hit one of the cyclists,’ Lyall said.

Another resident said: ‘There was a lot of blood and it was horrific to come across.’

The alleged domestic violence incident came at the end of a horror weekend across NSW, after three women were allegedly murdered inside their homes within a 12-hour period on Saturday.

NSW Police Deputy Commissioner Peter McKenna described the past two days as devastating.

‘It’s a horrific and tragic weekend and it’s like one that I don’t remember in my career,’ he told Nine’s Today.

‘When you balance out those three and plus the no-more-tragic situation than we had in the Blue Mountains. Put them all together and it’s unfathomable.’

Paramedics treated all three at the scene on Sunday before transporting them by road to Westmead Hospital and Westmead Children’s Hospital in critical condition, where they remain.

‘The two children and their mother are in a critical condition,’ Mr McKenna said.

Blue Mountains Police Area Command Commander Superintendent John Nelson (pictured) speaking to the media on Sunday

Emergency crews were called to Valley Heights after reports a woman and three young children had suffered stab wounds inside a vehicle (pictured)

‘The mother is the suspect in this matter, for domestic related homicide, and that investigation is ongoing.’

Hours after the incident, NSW Police Superintendent John Nelson said the father of the children had been notified.

He said the father had been at work when he received the call from police.

‘You can imagine receiving that tragic news,’ Supt Nelson told reporters.

He said the woman had not previously come to the attention of police and that investigators were not looking for anyone else in relation to the incident.

The woman is aged in her 40s, and the children are all under five years old.

All three have undergone surgery in hospital.

Supt Nelson praised the efforts of the ‘upstanding’ members of the public who responded to the tragic scene.

‘People are just going about a lovely Sunday afternoon and being confronted with this is traumatic and tragic for anybody,’ he said.

He said responding officers would not be spared the hardship and would have access to available support services.

Police said the weapon used and the circumstances surrounding the incident would form part of the investigation.

Blue Mountains councillor Darren Rodrigo on Sunday described the news as ‘absolutely horrendous and tragic’.

‘Our deepest love and condolences to the immediate family and our prayers with all the children involved,’ he said.

‘A massive thank you to the community members (who) intervened to provide medical assistance and to our first responders for their incredible support and courage during this time.’