A man is accused of repeatedly stabbing his partner with a box cutter just moments before he crashed into another vehicle and launched a frenzied attack on bystanders.
Police allege the 58-year-old crashed into another vehicle at the intersection of the Princes Hwy and Old Bush Rd at Engadine and turned on people who rushed over to help just before 9am Sunday.
The man allegedly stabbed a member of the public, who is in a serious but stable condition in hospital, as well as seriously injuring a police officer.
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In the chaos, the man self-inflicted serious injuries before his arrest.
He was taken to hospital in a critical condition and has since improved to serious but stable.
His partner, a woman in her 40s, is fighting for life in hospital.
Superintendent Donald Faulds said the pair both suffered “very serious” lacerations.
Two people were also injured in the crash.
Witnesses said they tried to keep the man in the area until police arrived.
He allegedly tried to run away and was tasered before he was arrested.
Faulds said the 58-year-old and his passenger, both from southwest Sydney, were in a domestic relationship but said police were not aware of a history of violence.
“We believe the female was being assaulted in the car whilst the male was driving the vehicle,” he said.
Witnesses reported seeing the car driving erratically and at high speed before it crashed, which is when police believe the alleged assault on his partner may have unfolded.
The alleged offender was known to police, Faulds said.
Several members of the public stopped to assist at the crash when the man emerged from his vehicle “covered in blood”.
Faulds said police believe the man intentionally injured himself after exiting his car.
Witness Nikki Cousins said she heard a car speeding before a “big bang” and rushed out to see the man holding a blade.
She said the man was ranting and threatening self-harm.
“He was quite manic,” she told 7NEWS exclusively.
She said the man had a “significant amount of blood” on his shirt.
Other witnesses said the man was heavily bleeding from his neck.
Bystanders attempted to keep the man in the area until police arrived.
One of the witnesses said they wanted to pin him down but he was armed.
“We couldn’t get to him because he had a switch-blade or something like that,” he said.
“I didn’t want anything to happen to the lady anymore.”
The witness said the group tried to keep the man away from his injured passenger and closed the car door to protect her.
Praise for hero witnesses
Police Minister Yasmin Catley said there was no ongoing threat to the community and commended the injured officer for their work.
“I don’t want to speculate at this point but I understand that that officer is OK,” she said.
“As people run from danger, police run towards danger.
“Their job is like no other and the work that they do on our streets, day in and day out, we are a very fortunate community to have the NSW Police and their dedication.”
Premier Chris Minns described the incident as “terrible”.
“I want to thank the brave NSW Police officers, first responders and members of the public for their actions,” he said.
“We are thinking of those innocent people who have been injured.”
Faulds echoed praise for the brave bystanders, saying they did “amazing work”.
“They just turned up thinking it was just a normal motor vehicle accident, so they obviously want to render assistance to both people, and then they were faced with a male armed with a box cutter,” he said.
“Quite frightening, but very, very brave.”