A six-year-old boy remains in a stable condition at the Royal Children's Hospital after emergency surgery late on Monday.

He was listed as being in a critical condition on Monday after a single-vehicle collision near Mortlake about 10am.

A hospital spokeswoman at lunchtime declined to provide information about if the boy had been placed in a coma following surgery.

The boy's mother was assessed and treated at the Warrnambool Base Hospital.

Earlier: Victoria police major collision investigation unit detectives are investigating after a car struck a tree in Mortlake on Monday.

The vehicle was travelling along the Hamilton Highway when it ran into a tree near Woodhams Lane shortly before 10am.

The female driver was transported by road to hospital with minor injuries.

A six-year-old boy was airlifted to hospital and is in a critical condition.

A three-year-old girl was taken to hospital with minor injuries.

Detectives are investigating to determine the cause of the crash.

Any witnesses or anyone with dash cam footage is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report at www.crimestoppersvic.com.au

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