A 36-year-old disqualified driver has been charged with manslaughter after a 12-year-old boy died after being pinned underneath the car outside a school at Hurstville in Sydney's south.

Key points: The 12-year-old boy was hit at 8:45am outside the Hurstville Public School

The 12-year-old boy was hit at 8:45am outside the Hurstville Public School The 36-year-old driver of the car involved has been charged with manslaughter

The 36-year-old driver of the car involved has been charged with manslaughter Ambulance officers described it as a "distressing scene for everybody"

Police said the car rolled on top of the child after he was hit about 8:45am, outside Hurstville Public School at the intersection of Forest Road and Lily Street.

Police said he was walking to Sydney Technical High School where he was a student.

NSW Ambulance said bystanders attempted to resuscitate the child before emergency services arrived at the scene.

A 36-year-old male disqualified driver has been charged with manslaughter and will appear in court on Saturday.

The driver was arrested at the scene and has been refused bail.

A white car looks to have mounted the footpath and crashed into the school's front gate.

Large green screens have been set up behind the car at the scene.

NSW Ambulance duty operations manager David Stride described it as a "distressing scene for everybody".

"The child has been pulled out from under the car and has been resuscitated by bystanders," Mr Stride said.

"We had five ambulances respond [and there was] also a medical team, so we had a doctor on scene.

Police at the scene where the boy was hit. ( ABC News: Selby Stewart )

"Unfortunately, the child was unable to be revived and was transported to Sydney Children's Hospital."

The boy was pronounced dead at hospital.

Mr Stride praised the actions of the bystanders, including an off-duty nurse who had performed CPR.

No-one else was injured in the incident.

The area has been blocked in both directions by police as detectives collect evidence from the footpath.

St George Police Area Command acting superintendent Craig James said a "terrible set of circumstances" had occurred.

"Despite the best efforts of concerned school citizens, parents and an off-duty paramedic, his life couldn't be saved," he said.

The man in custody has undergone blood and urine tests and will undergo further interviews, he said.

Superintendent James appealed for any witnesses in the area at the time of the incident to come forward.

"This is a tragic, tragic set of circumstances here this morning, so any further information that we can get that can assist with our enquiries, please contact Crime Stoppers," he said.