Video has emerged of a group of young men "flood surfing" on a torrential river in Auckland during the weekend's rainstorms.

Footage of the stunt shows a group of 15 young men surfing a swollen Rangitopuni Stream in Riverhead, north-west Auckland following last week's storms, which caused widespread flooding.

The men, aged 16 to 23, ride surfboards, kneeboards and an inflatable doughnut while holding wakeboard ropes tied to a bridge over the stream.

Tyran McRae, 22, told the Herald the group had all surfed the river before but never in such a raging torrent.

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The group's actions were "reckless" in some ways but there would always be an element of danger in extreme sports, McRae said.

The footage shows one man losing his grip on his rope and briefly getting sucked under another biscuiter. But despite the danger, only some of the riders are wearing lifejackets.

Lifejackets were available but it was a personal choice for people to wear them, McRae said.

All participants were capable swimmers, having grown up around rivers and beaches in north-west Auckland, he added.

The GoPro footage, filmed by McRae's girlfriend Micaela Challis, was posted to the Facebook page of the Chums, a clothing brand and collective of artists, rappers and extreme sports enthusiasts.