Stabbed Sydney teen in critical but stable

Julia Carlisle

A 16-year-old boy has undergone surgery after being repeatedly stabbed in a car park in Sydney's trendy inner west by a stranger in what police say was a "ferocious" attack.

The teen was buying groceries at the Balmain Woolworths supermarket with his younger brother, aged 14, before the attack at a car park on Darling Street about 7pm on Thursday.

He suffered wounds to his upper body and hand and was taken to Royal Prince Alfred Hospital where police on Friday said he remains in a critical, but stable, condition following overnight surgery.

Police are keen to speak with a red-haired man who was wearing a red jacket and a woman who they believe could help them piece together what happened.

A witness said she heard the boy cry out before she approached him to find him surrounded by blood.

"I just saw some kids screaming and at first I thought they were mucking around," the woman told Nine News.

"Then I heard him just scream out 'I've been stabbed, I've been stabbed, help me'.

"I walked over and there was just blood all over the floor. He said 'I didn't know where he came from or who he was, he just came out of nowhere."

Inspector Gary Coffey said it's not believed the attacker and the teenager knew each other.

He said police are eager to speak with the teenager once his condition improves.

"It's a pretty ferocious attack and certainly it's not something that would normally occur in this area," he told reporters at the scene.

The man is described as being caucasian, about 182cm tall and with ginger hair, while there is no description of the woman.