A group of lifeguards swimming off the coast of New Zealand may have been saved from a shark attack recently by several protective dolphins that helped to hold the predator at bay.

Lifeguard Rob Howes said he and three female lifeguards were on a training swim about 100 metres off Ocean Beach near Whangarei on the North Island.

About halfway through the swim, a pod of dolphins "came steaming at us" and started circling, startling the swimmers, he said.

Howes said he was unnerved by speed of the approach, thinking perhaps it was a group of aggressive males or dolphins protecting their baby.

The dolphins bunched the four swimmers together by circling about 4-8 centimetres from them, and slapping the water with their tails for about 40 minutes.

Howes said he drifted away from the main group when an opening occurred. One large dolphin became agitated and submerged toward Howes, who turned to see where it would surface.

That, he says, is when he saw a great white shark about two metres away in the beach's crystal clear waters.

"The form came and travelled in an arc around me. I knew instinctively what it was," he said.

When the shark started moving toward the women, including his 15-year-old daughter, the dolphins "went into hyperdrive," said Howes.

"I would suggest they were creating a confusion screen around the girls. It was just a mass of fins, backs and ... human heads."

The shark left as a rescue boat neared, but the dolphins remained close by as the group swam back to shore. At no point did the shark break the surface of the water, remaining near the bottom, he said.

Howes said he didn't tell the rest of the group about the shark until the next day.

"I came out of that water and I was stunned. I had no idea how to relay what had happened and how to deal with it," said Howes.

While this all happened on Oct. 30, the swimmers didn't tell their story until recently.

He says he spent the next few weeks talking with dolphin experts about the incident, who told him it wasn't unusual for dolphins to protect swimmers.

There've been a number of great white sightings in the area at this time of year, mainly because they come into the harbours to give birth, said Howes.