Beach-goers at Omaha Beach were forced from the surf yesterday after the second shark sighting in three days at the popular spot north of Auckland.
At least 80 people were told to get out of the surf after lifeguard Deborah Collings, who saw a shark swim under her surfboard, triggered the alarm at about 2pm.
Lifeguards erected warning signs and combed the beach on quad bikes, telling swimmers to get out of the water.
Kris O'Neill of the Climatech Regional Lifeguard Service said about half a dozen sharks, possibly bronze whalers, were seen, some as close as 20m offshore.
He said it was strange the sharks appeared close to the shore at about the same time of day that a 4m shark - thought by some to be a bronze whaler and others to be a tiger shark - attacked a lifeguards' inflatable rescue boat at Omaha on Monday.
Mr O'Neill, 26, and colleague Lauren Johnson, 19, were checking reports of sharks near the beach at about 2pm when the shark sank its teeth into one of the boat's rubber pontoons, causing it to deflate.
Mr O'Neill did not know why the sharks were so close to shore.
"But there's a lot of bait fish in the water at the moment. We see lots of schools of fish and that could be one of the reasons.
"We were not keen to chase the sharks away, especially after what happened the other day."
Auckland student Dianne Ruela, 31, who stayed knee-deep in the water after warnings were posted yesterday, said: "It was actually quite terrifying to know that [the sharks were nearby]. We had no idea that they were right there."
Lifeguards at Whangamata also spotted a shark yesterday but decided against alerting swimmers as they felt it was small, 1.5m long, and far enough away to not be a danger.