A poisonous yellow-bellied sea snake related to the cobra has been spotted in the waters of Tauranga Harbour.

Omokoroa resident Shane Davies was out fishing in the harbour on Tuesday evening when he spotted the snake near the Plummers' Point boat jetty.

A poisonous yellow-bellied sea snake has been spotted in Tauranga Harbour.

'Me and my son were fishing there all night and one came wriggling around by the jetty there.

'We told a few people but no one really believed us, it was all yellow and wriggling across the top of the water, like a snake would on sand.”

NIWA – the National Institute of Water and Atmospheric Research is warning people to beware of the snake while swimming this summer.

Principal scientist Malcolm Francis says while the snake usually preys on fish, bites to humans can cause paralysis or renal damage if the snake's venom it finds its way into the human body.

Shane says the difference between sea snakes and eels is that sea snakes travel on the surface of water and complete the ‘S' wriggle.

'That was right in the harbour, right close to the boat ramp. It was about one metre long, so not small, and it wasn't scared of us.

'We went down and were poking a stick at it and it wriggled towards us, so we had to jump back because the tide was coming over the jetty.”

The yellow-bellied sea snake is related to the Cobra and has been sighted as far south as the Cook Strait, but is most common in the northeast part of the North Island.

Malcolm says the snake lives in the open sea and travels with ocean currents.

'They live near the surface, hang around with logs and drifting seaweed, and feed on the fish that aggregate in those areas.”

Swimmers are urged to keep their distance if they spot the yellow bellied snake.