A two-year-old girl who was locked in a running car had to be freed by paramedics.

She was among 27 people treated across NSW for heat-related illness on Saturday.

At 2.42pm (AEDT) on Saturday, paramedics were called to the Central Coast township of Buff Point to free the two-year-old.

A NSW ambulance service spokeswoman told AAP the child had been locked in a running car inside a garage on Buff Point Road.

She was freed from the car and after examination did not require further treatment.

Police were alerted to the incident, the spokeswoman said.

The Central Coast was worst affected by heat-related illness, with 13 cases.

In the Sydney and western NSW regions, a total of 14 people were treated.