Whitebaiters warned a man against kayaking across a river mouth in treacherous seas with his 4-year-old daughter on board.

But the 44-year-old father did not listen, they said. He and the girl - neither of whom was wearing a lifejacket - were swept out to sea when the kayak capsized at the Tukituki River mouth in Hawke's Bay on Sunday.

Whitebaiter David Goodman said: "The guy fishing beside us mentioned to them it wasn't a wise decision to cross where they were crossing, but they didn't take the advice and that was the end result - near death."

The strong currents overturned the kayak and dragged the pair out to a shingle bar, which kept them from drifting further out to sea.

Seeing the kayak flip, Mr Goodman grabbed his longboard and headed out to help.

"I realised there was a child involved without a lifejacket. It was priority to get her taken care of."

He put the girl, who was close to hypothermic, on his board and paddled her to shore.

He then returned to the shingle bar to help her father and a friend who had also gone to help.

"The father was pretty tired and not confident to swim, so I gave him the longboard and sent him on his way."

Mr Goodman and the other man swam behind him back to shore.

Once the pair were safely in the ambulance, Mr Goodman headed back to his whitebaiting.

He did not consider himself to be a hero.

"Apart from waiting for the coastguard, there wasn't any other way of getting them back. It's nothing to do with heroism, it's just wanting to help."

- © Fairfax NZ News