Driver fights for life after crashing into tree during police pursuit

A driver is tonight fighting for his life after crashing into a tree in an allegedly stolen car in Melbourne's west this morning.

Police attempted to intercept the black BMW when it failed to stop for police about 11.45am in Melton South.

After a short pursuit, the BMW left the road and crashed into a tree on Exford Road. Police estimate it was travelling in excess of 100km/h.

The male driver, believed to be aged in his mid 20s, was trapped for 15 minutes before he was cut free. He suffered critical injuries and remains in hospital.

Witness Bruce Conche told 9NEWS he was driving his truck when he came across the crash scene.

"It was pandemonium, I was trying to keep him alive," he said.

The vehicle was allegedly stolen in 2014.

Acting Superintendent Kerin Moloney said he believed the police acted appropriately in the circumstances.