Muriwai Beach near Auckland was closed after the fatal attack, one of only about a dozen in New Zealand in the past 180 years.
Police recovered the body of the victim, identified as Adam Strange, a 46-year-old television and short film director, the New Zealand Herald said. Strange won a Crystal Bear award for best short film at the 2009 Berlin Film Festival, according to his company’s website.
The newspaper said his family issued a statement expressing their shock and requesting privacy.
Pio Mose, who was fishing at the beach, told the Herald he saw the swimmer struggle against the huge shark. He told the man to swim to the rocks, but it was too late.
“All of a sudden there was blood everywhere,” Mose said. “I was shaking, scared, panicked.”
Police inspector Shawn Rutene said Strange was swimming about 200m offshore when the shark attacked. He said police went out in inflatable lifesaving boats and shot at the shark, which they estimated was between 3.6m to 4.2m long.
“It rolled over and disappeared,” Rutene said, without saying whether police were certain that they had killed it.
About 200 people had been on the beach at the time of the attack. Police said Muriwai and other beaches nearby have been closed until further notice.
Police did not say what species of shark was involved in the attack. Clinton Duffy, a shark expert with the department of conservation, said New Zealand is a hotspot for great white sharks, and other potentially lethal species also inhabit the waters.
However, attacks are rare. Duffy estimated that only 12 to 14 people have been killed by sharks in New Zealand since record keeping began in the 1830s.
“There are much lower levels of shark attacks here than in Australia,” he said.
Duffy added that, during the southern hemisphere summer, sharks often come closer to shore to feed and to give birth, although that does not necessarily equate to a greater risk of attack.