A woman who died alongside two of her children when their car plunged into the Tweed River in northern NSW has been described by police as a "remarkable" mother who perished while trying to save her family.

Stephanie King died trying to save her children from their sinking car. ( Supplied: Facebook )

On Tuesday, police retrieved the bodies of Stephanie King, 43, and two of her children, Jacob, 7, and Ella Jane, 11, after the incident at Tumbulgum on Monday afternoon.

Ms King's other daughter, Chloe May, 8, managed to escape the car as it left the road and landed in the river.

Superintendent Wayne Starling believes the young girl escaped the car with the help of her mother.

"I have no doubt she's a hero," he said.

"She would be alive today if she wasn't trying to save her children."

He said divers found Ms King holding one of her children and she appeared to be trying to get them out of the car as she passed away.

He said the ordeal had been "very traumatic" for Chloe May and they were doing everything they could to help her.

"She's a very brave girl," he said, adding that she has suffered injuries to her feet while escaping the vehicle.

Premier Gladys Berejiklian has offered her condolences to the family of the victims.

"Especially I want to express our condolences to the young girl who miraculously escaped the crash with her brother and sister and she bravely ran to raise the alarm," she said.

"We cannot imagine the trauma this little girl and her family and the entire community is going through at this time and our thoughts and prayers are with all of them."

A crane was used to remove the car from the Tweed River. ( Fairfax Media: Kate Geraghty )

Very difficult for divers to retrieve bodies

Map Tumbulgum, NSW

Superintendent Starling said the rescue had been incredibly difficult due to the dark, debris-filled river and the four police divers could only locate the vehicle by hand due to the murky waters.

"It was very difficult and dangerous to extract the mother and children from the vehicle as a result of the conditions," he said.

"They were very worried about the vehicle moving.

"These police divers put their lives at risk to recover the bodies today."

Sorry, this video has expired Police divers search for the car that disappeared in a flooded river in Tumbulgum

Road barricades possibly moved

The road the family had been driving on was closed due to mud and debris, Assistant NSW Police Commissioner Jeff Loy said yesterday.

Police taped lines at the Tweed River at Tumbulgum on Tuesday morning. ( ABC News: Jade MacMillan )

But that statement was disputed by at least one local resident, Rob Stuttle, who told the ABC he had driven on the road the night before the family went missing.

Mr Stuttle, a pastor, said he wanted to "set the record straight".

"As far as I know, the road wasn't closed, and I don't want people to think it was the woman [driving] being irresponsible," he said.

In response, Superintendent Starling said on Tuesday that when police arrived on the scene, the road was closed but he was mindful that sometimes people moved barricades.

"They [the barricades] weren't on the road last night but were moved back this morning according to a lot of people," he said.

"We are not putting any blame on the mother," he said.

Local resident Dave Johnstone said the family had been helping flood victims before the accident.

"Apparently they were down here helping everybody else and ... cleaning up and were on their way home," he said.