A woman has thrown herself onto the bonnet of a car while trying to stop her friend's baby being taken during a dramatic carjacking outside a school in Melbourne's north.

The girl's mother and a friend were standing outside the car, a Mercedes, waiting for children to finish school on Ross Street, Coburg about 3:00pm.

"A male and a female approached the car of the victim, the male got in the car and drove off straightaway," Senior Constable Virginia Creece from Victoria Police said.

"The friend of the victim actually got on the bonnet of the car and attempted to stop the male from leaving.

"I think she was on the car for about 400 metres before she fell off the car.

"She stated that during this time she was screaming at the male who was driving away and trying to get him to stop but he refused to stop and kept going."

The man dumped the car in Haig Avenue, Brunswick, about 45 minutes later and told a passerby about the girl in the back seat.

"When the male left, he told this witness that he had a baby in the car and he didn't know what to do with it," Senior Constable Creece said.

The pair had arrived in a silver Camry, and the woman drove away as soon as the incident happened.

Police are still searching for the offender, who is described as being of European appearance with dark wavy hair, a light coloured top and dark pants.

'Baby wasn't fazed but mum hysterical'

CCTV footage showed a man getting out of a silver Camry before the incident. ( Supplied: ABC News )

She said the mother was "hysterical" about the situation.

The car also drove over her foot when it was taken.

The car keys were inside the car when the male jumped in and he instantly locked the doors.

"It was quick action ... but also a dangerous act on [the friend's] part but I understand her distress that she needed to get into the car," Senior Constable Creece said.

She said it was most likely a random act and believed the man dumped the car quickly once he realised he had the child.

The baby was "not even fazed by the whole thing", Senior Constable Creece said.

The mother's friend was also not seriously injured.

In August, a five-year-old girl was inside a luxury car when it was stolen from the driveway of the family home in Wyndham Vale, and was later found in Geelong.