A senior lifeguard at Piha beach, west of Auckland, says lifeguards had to rescue teenagers taking part in a surfing lesson in unsafe conditions on Monday.
Duncan Clark says he was called to the beach and saw about 11 people paddling frantically in a rip and swells of up to three metres.
Describing the scene as "disorganised chaos", he says he and other lifeguards pulled one frightened young man into a rescue boat.
Piha Surf School instructor Phil Wallis says the rescue was unnecessary. He says the students were taken into the rip so they could learn how to get out of it.
But Mr Clark says that, in Monday's conditions, a lesson should not have been held in one of the most treacherous rips in New Zealand.