A man has been flown to hospital with serious injuries after the allegedly stolen car he was driving smashed into a tree during a police pursuit in Melton South.

Police were at the scene on Exford Road investigating the crash on Monday afternoon.

It is believed police tried to stop the black BMW about 11.45am on Monday, but the driver sped off.

The BMW was allegedly stolen.

"Police activated their lights and sirens and initiated a pursuit before the car crashed into a tree," police said in a statement.

An Ambulance Victoria spokeswoman said the male driver had been airlifted to The Royal Melbourne Hospital in a critical condition.

Earlier this month, the state's senior traffic officer flagged "substantial changes" to Victoria Police's pursuit policy.

But road policing Assistant Commissioner Doug Fryer said the changes would remain secret.

"Now it is time to put the genie back in the bottle, to put the cloak of mystery over when we will and won't engage so crooks don't know what they will and won't get away with," Mr Fryer said.

"We don't broadcast how we conduct investigations into counter-terrorism, organised and serious crimes ... nor should we further educate the criminal element of what we can and what we won't do in police pursuits."

But in an internal video obtained by radio station 3AW, Mr Fryer told police they could pursue for minor traffic and property offences if they could cause a serious risk to the public.

This included, he said in the video, armed offenders and criminals fleeing from aggravated burglaries and those who drive at police and ram police cars.

With Tammy Mills

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