A HORRENDOUS overnight crash in Sydney's inner west has left a man fighting for his life and a family of six seriously injured.

Emergency crews rushed out to reports of a head-on collision between a Suburu Impreza and a Toyota Hiace mini-van at the intersection of Victoria Rd and Salter St in Gladesville at 11.30pm last night.

At the scene, they worked for 45 minutes to free the 25-year-old driver of the Suburu from the wreckage of his car.

He has been taken to hospital in a critical condition with a broken leg and internal injuries. He will also undergo mandatory testing.

The six family members in the Hiace were all injured in the crash, and were taken to the Children's Hospital at Westmead, Royal North Shore Hospital and Royal Prince Alfred Hospital with various injuries but all in a stable condition.

The 60-year-old driver is in a serious but stable condition, with a fractured sternum and ankle.

A 44-year-old man and 44-year-old woman, along with three children - two boys 16 and 17 and a girl, 13 - are all "under observation", according to NSW Police.

NSW Ambulance inspector Jordan Emery said heavy rain could have been a factor in the crash.

"It appears that the wet road surfaces have contributed to this very serious accident. There's substantial damage to both vehicles," he told Seven News.

"We're really reminding people to slow down on the roads in wet weather. It's critical for your safety and the safety of other road users."

Police from Ryde Police Area Command are investigating and appealing for witnesses.

- more to come