A woman in her 20s was trapped in her car for over half an hour after the smash, which occurred on Ballarto Road, in Junction Village, around midday on Thursday.

Firefighters managed to free the woman after cutting off the roof of her crushed car.

The woman was flown to The Alfred in a serious but stable condition, according to an Ambulance Victoria spokeswoman.

The four children and a woman, believed to be in her 60s, were taken to Dandenong Hospital in a stable condition.

Country Fire Authority district 8 duty officer Cliff O'Connor said it was remarkable the injuries weren't more serious.

"Both cars are pretty badly damaged, so it was a close-call," he said.

"Firefighters did a brilliant job getting the woman out of a heavily crushed vehicle and it was lucky the kids weren't badly harmed." 

With Broede Carmody