Aditya Raut has become the youngest person to swim Cook Strait.

The 11-year-old had to battle 2m waves whipped up by a southerly.

The swim was not publicised because organisers feared the 43kg boy, who travelled from Pune in India for the swim, might not make it.

Swim co-ordinator Philip Rush, who has watched over most Cook Strait swims, said Aditya showed great determination in tough conditions during the swim on Monday.

"His parents were sick the whole way across [in the support boat]," Mr Rush said.

"A lot of people would have pulled out."

Aditya swam the 26km from north to south - Ohau Point to Cape Koamaru - in 9 hours 9 minutes. Allowing for tides, he covered about 40km.

Until yesterday, 13-year-old Upper Hutt schoolboy John Gatfield was the youngest Cook Strait swimmer.

The accidental swimmer - Aditya only took up swimming after physiotherapy following a broken leg at the age of six - spent yesterday recuperating and eating his mother's potato curry soup.

- NZPA