Mother facing charges for allegedly leaving her nine-month-old baby alone in the car

Police are expecting to charge a mother who allegedly left her nine-month-old baby sleeping alone in a car that was parked outside an apartment block in Sydney's west.

Witnesses who called triple-0 claimed the child was left alone in the vehicle in Lakemba for at least 30 minutes on Tuesday night before police arrived and broke into the vehicle.

The baby boy was distressed when officers rescued him from the back seat of the vehicle on Lakemba Street about 10pm, police said.

A NSW Police spokeswoman said a short time after police rescued the child, his 31-year-old mother arrived.

Paramedics were called and assessed the baby, who was not injured. He was left in the care of his mother.

Police said an investigation into the incident had been launched, and the mother is expected to be issued with a future court attendance notice.

However, the police spokeswoman could not say what charge the woman would be facing.

Police said it was against the law to leave a child locked in a car unattended, and anyone convicted of doing so could be fined up to $22,000 under the Children and Young Persons (Care and Protection) Act.

Last year, 19 people in NSW were charged for causing distress or injury after leaving a child in a vehicle.

With Sydney heating up this week, police warned that temperatures in a closed vehicle could rise to dangerous levels in just a matter of minutes.

Police said that, on a hot day, the temperature inside a parked car could rise to 30 or 40 degrees above the outside temperature within 15 minutes.