Police on hunt after Sydney teen stabbed

A Sydney teen is fighting for life after being repeatedly stabbed outside a unit block in the city's west, with police saying it doesn't appear a random attack.

Emergency services found the 17-year-old with multiple wounds in South Granville just after 9am on Thursday.

He was taken to Westmead Hospital in a critical condition, while the police dog unit and helicopter have joined officers in the search for the attacker.

NSW Ambulance Inspector Jennine Kiely said the scene was confronting.

"It was quite a disturbing scene when paramedics arrived because we were confronted with a man who had lost a lot of blood," she said in a statement.

"We did everything we could to stabilise him before he was transported."

Detective Superintendent Darryl Jobson later said the investigation was still in its early stages and police didn't yet have a suspect.

"From the inquiries that we've made so far it tends to indicate that this incident is unlikely to be a random attack," he told reporters.

He said they were still looking for the weapon "but it is quite obvious that we are looking for a sharp instrument".