Two children have died after a car ploughed into a classroom at a school in south-west Sydney, while 21 others were injured in what police believe was a tragic accident.

Key points: Five students were taken to hospital, where two died

Five students were taken to hospital, where two died The 52-year-old female driver of the SUV was not injured

The 52-year-old female driver of the SUV was not injured NSW Ambulance described the scene as "carnage" and "chaotic"

Ambulance New South Wales said 16 of its vehicles were called to a "scene of carnage" at Banksia Road Public School, in Greenacre, about 9:45am.

There were 24 children in the classroom at the time.

Two boys, aged eight, were critically injured. They were taken to Westmead Children's Hospital where they died.

Three other children were taken to hospital but most other students from the classroom have minor injuries and were assessed at the scene, paramedics said.

The ABC understands the 52-year-old female driver of the Toyota Kluger was dropping off a child at the time.

The driver of the car was taken to hospital for mandatory blood and urine tests. ( AAP: Dean Lewins )

She was not injured and was taken to hospital for mandatory blood and urine tests.

There were 17 children and one adult female teacher assessed on scene.

Distressed children at scene of 'horrible accident'

NSW Ambulance Superintendent Stephanie Radnidge said the children who died had "multiple traumas".

"It is very, very hard because we are parents ourselves," she said.

"We are human beings. But we are highly trained and the best care was delivered this morning to those injured at this site."

Sorry, this video has expired Banksia Road Public School children killed after car ploughs into classroom

Superintendent Radnidge said the scene was "quite chaotic".

"Obviously it was a scene of carnage," she said.

"There were a number of distressed and overwhelmed children and teachers at the scene of a horrible accident.

"There was obviously pandemonium."

Two chaplains were among the number of NSW Ambulance staff who attended.

An aerial image showing where the car crashed into the classroom at Banksia Road Public School. ( Google Maps )

'We don't believe this was an intentional act'

NSW Police Acting Commander Stuart Smith said it was unclear if the woman had a relationship with the school.

"We don't believe this was an intentional act," he said.

He said family members of the two dead students were receiving counselling.

"It would be only speculation that we believe we know what caused this event at this time," he said.

NSW Police and ambulance officers at Banksia Road Public School this morning. ( Twitter: @Zara_James9 )

Education Minister Rob Stokes and Premier Gladys Berejiklian visited the scene but did not speak to the media.

In a statement, the Minister thanked the school staff and emergency services personnel for their "commitment and fortitude".

"I cannot begin to comprehend the sadness being felt by the parents and families of the two young boys who have died in today's tragic accident at Banksia Road Public School," he said.

"My thoughts and prayers are with their families and the entire school community."

A crime scene has been set up and police from the Bankstown Local Area Command are on site.