Move over Rover, let Flipper take over. News from New Zealand suggests man's best friend is in fact the bottlenose dolphin.

It emerged yesterday that four swimmers were saved from a great white shark by a pod of altruistic dolphins, who swam in circles around them until the humans could escape.

Rob Howes, a British-born lifeguard, had gone swimming with his daughter, Niccy, and two of her friends off Ocean beach near Whangarei on the North Island, when the dolphins suddenly appeared. At first, he thought the mammals were being playful, but he soon realised the danger the swimmers were in.

"They started to herd us up, they pushed all four of us together by doing tight circles around us," Mr Howes told the New Zealand Press Association.

He tried to drift away from the group, but two of the bigger dolphins herded him back - just as he spotted a three-metre [10ft] great white shark heading towards him. "I just recoiled," he said. "It was only about two metres away from me, the water was crystal clear and it was as clear as the nose on my face. They had corralled us up to protect us."

The dolphins kept their vigil for 40 minutes until the shark lost interest, and the group could swim 100m back to the shore.

Another lifeguard, Matt Fleet, on patrol in a lifeboat, saw the dolphins circling the swimmers and slapping their tails on the water to keep them in place. He told the Northern Advocate newspaper that he also had a clear sighting of the shark. "Some of the people later on the beach tried to tell me it was just another dolphin; but I knew what I saw," he said.

Although the incident happened on October 30, the swimmers have only just spoken of their rescue.

Ingrid Visser, of Orca Research, an environmental group, said the dolphins' behaviour was understandable, as they attack sharks to protect themselves and their young, and similar incidents had been reported round the world. "They could have sensed the danger to the swimmers, and taken action to protect them," she said.