A rescue helicopter has flown a newborn baby and other children to safety from a farm cut off by floodwaters on the NSW mid-north coast.

The Westpac Lifesaver Helicopter was returning to pick up other family members at Mount Seaview Reserve on Saturday afternoon when it was diverted to rescue a woman trapped in her car by floodwaters.

Helicopter spokesman Steve Leahy told AAP that rescue got underway at around 4.30pm (AEDT).

He said a family of up to eight needed to be evacuated from their farm about 30km west of Wauchope and the helicopter on its first trip had flown the baby and other children to Port Macquarie.

"The farm was isolated by floodwaters and the newborn baby was a little bit sick or in distress."

The flooding along NSW's north and mid-north coasts has claimed the lives of a teenage boy who was swept into a drainpipe in Kew on Friday night and a man whose body was found in his submerged car northwest of Grafton.

Police are urging motorists not to drive into floodwaters following the man's death and the rescues of at least 15 other people from floodwaters.

"It is dangerous for them and for those who have to rescue them," NSW Police Assistant Commissioner Alan Clarke said.