A man has allegedly gone on a stabbing rampage at Engadine in Sydney's south after a crash on the Princes Highway.
The 58-year-old allegedly slashed his partner and injured four others including a police officer.
Bystanders stepped in to protect the woman as the alleged attack played out in front of families.
The 58-year-old man in a white T-shirt could be seen ranting after allegedly stabbing his female passenger and himself.
In footage he can be seen wandering on the road by the crashed car looking confused, and shouting and swearing.
Traffic had come to a standstill.
Standing at the front of the car near him was Cronulla Sharks chairman Steve Mace.
"[I]Heard the guy screaming - in the drivers but his wife or partner screaming louder, so I ran to the passenger, tried to open the door - try to jam it open and I see he's just slashing her," he said.
The man was armed with a box cutter but Mace and another man still tried to pull the woman from the car.
"I was trying to drag her out of the car, another guy copped a gash poor fella," Mace said.
In a car directly behind was a family, who watched as Mace and several others tried to subdue the man before police arrived.
A police officer arrived and chased the man.
The officer caught him and fired his Taser, but during the arrest the officer was stabbed in the wrist.
The 28-year-old was taken to St George Hospital in a serious but stable condition.
"He was just lying on the side of the road in the recovery position - his hand was quite badly cut," one witness said.
The woman, in her 40s, remains in a stable condition in hospital.
The other man who was hurt, who is in his 40s, is also stable in hospital.
Earlier CCTV caught the man driving his car erratically.
Then on the Princes Highway he crashed into a blue sedan.
The man and woman were in a relationship, police said.
Police allege she was stabbed in the moments leading up to the crash, which is why he was driving so erratically.
A total of six people were injured - with four stabbed.
It started about 9am at the intersection of Old Bush Road when the man's partner reached for the dashboard.
Members of the public were praised for their selfless acts of bravery.
"They've just turned up thinking it was just a normal motor vehicle accident, so they've obviously gone to render assistance to both people, and then they were faced with a male with a box cutter, quite frightening, but very, very brave on those people's behalf," Superintendent Don Faulds said.
The man is known to police.
He is in a critical condition at Liverpool Hospital.
NSW police minister Yasmin Catley told reporters that there was no ongoing threat.
"Obviously that investigation is under way, I've been advised that the person of interest has been arrested," she said.
"There is no threat to the community. I want the community to know there is no threat whatsoever."
All northbound lanes were reopened, along with one of three southbound lanes.
All diversions were lifted, but motorists were warned to allow extra travel time.
Support is available from the National Sexual Assault, Domestic Family Violence Counselling Service at 1800RESPECT (1800 737 732).