Several people have inadvertently put themselves in danger while swimming at Morgan St Beach at the North Mole in Castlecliff, and surfers have had to rescue them.

The rescues have led local surfers to post a warning about the rip at that section of beach.

Surfer Melina von Kwiatkowski was testing her new surfboard at the beach on Monday when she heard swimmers calling for help.

"I was by my car and I wondered what was going on at first - I thought it was a shark attack or something."

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Ms Kwiatkowski said two teenage girls were caught in a rip, and they were taken by surprise when they got sucked into the deeper water.

"One minute they were able to walk in the water, and then they were pulled out by the current," she said.

Another swimmer called out to one of the girls and told her how to get back to the shallower water, while Ms Kwiatkowski helped the other back to safety with her board.

Wanganui Board Riders have issued warnings to swimmers at the North Mole on their Facebook page with a post at the end of December.

"Just a friendly reminder that if you swim at Morgan St beach this summer, please be very aware of the dangerous rip that runs along the side of the rocks. "It is always there and can be powerful."

The message was posted after "three near drownings at Morgan St beach" and the group warned against swimming when the tide was going out.

Wanganui Surf Lifesaving does not have resources to patrol the south end of the beach adjacent to the North Mole and prefers people to swim at the northern end of the beach in front of the surf club where there are regular patrols.

Lifeguard Sophie Couper, on duty at the beach this week, said swimmers in the patrolled area have been showing a lot of caution and enjoying their holiday time at the beach.

"They have been really listening to us, and we have had a lot of regulars coming every day," she said.

Water Safety New Zealand has reported that 113 people died from drowning in 2015 - a 26 per cent increase from the 2014 total.

An ACC and Water Safety New Zealand campaign launched in December urges people to "Stop and Think Before You Go Near the Water" and Water Safety New Zealand chief executive Matt Claridge says if everyone did that the drowning toll would come down.