Six-year-old boy 'critical' after being pulled from rough seas in NSW

A six-year-old boy has been flown to hospital in a critical condition after being pulled from treacherous seas on the NSW north coast.

The boy was swimming with family in shallow water near a rock wall at the unpatrolled South Ballina beach when his older brother got into trouble and his father swam to help.

They returned to find the younger boy floating face down in the water, Surf Life Saving Far North Coast duty officer Jimmy Keough told AAP.

His body was dragged onto the break wall where fishermen and others began CPR.

Surf life savers and paramedics arrived to take over before he was flown by helicopter to Gold Coast Hospital in a critical condition.

A spokeswoman for the hospital could not provide an update on the boy's condition.

It comes amid a severe weather warning for the region as thunderstorms and heavy rains work their way south from Queensland, where five people were killed by floodwaters on Friday.

Mr Keough said the weather had caused "treacherous" beach conditions in the area with large waves, powerful rips and coastal erosion.

"It's an unpatrolled beach, it's a very remote location, and it would have been treacherous at the time of the incident," he said.

The only active life saving service in the area is some 30km north at the main beach in Byron Bay, which was closed on Saturday.