A New South Wales mother has been put through a terrifying ordeal after her car was stolen with her baby inside.

Police have arrested a 33-year-old man after he allegedly stole the car from outside a childcare centre at Telopea on Thursday afternoon.

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But they have praised the actions of a good Samaritan who rushed to the mother’s pleas for help.

Rob Burgess told Nine News he heard the mother screaming and took down a description of the car before starting a search of the nearby area.

He found the baby lying unharmed on the side of the road in nearby Dundas.

“The noise coming out of it was incredible,” Mr Burgess said.

“Freezing cold weather, cold wind, for someone to do that is just heartless.”

He said the child’s loud crying failed to alert anyone from neighbouring homes.

Police found the suspect driving the stolen car in Parramatta.

He was charged with taking a motor vehicle with an occupant on board and abandoning or exposing a child under seven years to danger of serious injury.

He was refused bail to appear in court.