Four kids ‘incredibly lucky to survive’ after BMW smashes into family car

A high-speed police pursuit has ended when a driver crashed into a vehicle carrying four young children and their parents in Sydney.

Authorities said it's incredibly lucky no one was killed when a BMW smashed into a family's Mazda just after 8.30pm yesterday on the M5.

The police pursuit began when the driver of a BMW failed to stop after being pulled over for a random breath test.

The driver dodged authorities, speeding between cars on the busy motorway.

The BMW eventually hit a Honda, with two people inside, before smashing into the Mazda.

"I was driving in the middle lane and I looked in my rear-view mirror and I saw a car that was speeding really fast and then out of nowhere it hit the car that was right beside me," a witness told 9NEWS.

"It was a huge crash and then a different car started spinning, smoke everywhere."

A passenger in the BMW was questioned by police but later released.

The driver fled the scene on foot and has not been arrested.

No one else was injured in the crash.

Anyone with information is being urged to contact Crime Stoppers on 1800 333 000.