Four people, including a police officer, have been injured in a stabbing attack following a crash on a major Sydney highway.
Two vehicles collided at the intersection of the Princes Hwy and Old Bush Rd at Engadine just after 9am Sunday, police said.
Witnesses said the car was travelling at speed before the crash.
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Nikki Cousins said she heard a “big bang” and rushed out to see the driver of one of the cars 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.”
Police said a woman, understood to be a passenger in the crashed vehicle, was found with multiple stab wounds.
The witness said the group tried to keep the man away from her and closed the car door to protect the injured woman inside.
Police said they arrived to find a man, who appeared to be suffering stab wounds, allegedly running from the crash scene.
Officers used a taser to arrest the man.
A male police officer suffered a serious laceration to his left wrist believed to be during the arrest, police said.
Police said a fourth person was also found injured.
It’s unclear at this time what their involvement is in this incident.
All four people have been taken to hospital.
Police Minister Yasmin Catley said there was no ongoing threat to the community.
Catley 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.”
The highway has been shut in both directions between Farnell Ave at Loftus and Heathcote Rd at Engadine.
Motorists are advised to allow for extra travel time as traffic is heavy and diversions are in place.
All motorists being diverted via Old Princes Hwy, The Grand Pde, Linden St, River Rd, Bangor Bypass, New Illawarra Rd and Heathcote Road Rd in both directions