More harrowing details are emerging after the death of a three-year-old Sydney boy who was left alone in a hot car for hours on Thursday.

The boy was unable to be revived after being found in the vehicle on Railway Parade in Glenfield in the city’s south-west on Thursday afternoon.

Police were told the child had been in the car throughout the day.

It came as the NRMA issued a grim warning after revealing the shocking number of children rescued from similar potentially deadly situations – and warned parents to be vigilant.

NRMA spokesman Peter Khoury said the agency had rescued 213 children from hot cars across NSW and the ACT in January – the highest number in the past five years. The number of rescues jumped to 501 if unattended pets were included.

“The temperature inside a vehicle can double from outside in a matter of minutes,” spokesman Peter Khoury said.

“In a very short time, a child can become dehydrated. That can lead to organ failure and that can lead to catastrophic consequences.

“That is clearly no place for a child, even for a few minutes.”

Figures for 2022 were even bleaker. Mr Khoury said 1882 children  4267 children and 2385 pets had been found locked in vehicles that year – a 10-year record.

“It’s highly dangerous all year round, regardless of the weather,” Mr Khoury said.

“But it’s particularly dangerous during Australian summers.”

In Glenfield on Thursday, the child’s 45-year-old father reportedly smashed his car’s window to retrieve his son before collapsing to the ground, wailing and banging his head. In some footage, he was seen with blood on his hands and arms.

The man was later taken to Campbelltown Police Station to be interviewed.

On Friday, police said he had been released from custody while officers continued investigating the death.

Campbelltown, near Glenfield, hit a top temperature of 33.4 degrees at 4.30pm Thursday, according to Bureau of Meteorology data.

Floral tributes and soft toys were left at the scene throughout Friday.

-with AAP