(CNN) -- Four people have died and four others remain missing from a fishing boat that sunk near the southern tip of New Zealand after being hit by a "rogue wave," the police said Friday.
Rescuers found one survivor on Thursday from among the nine people who were on board Easy Rider, the 40-foot fishing vessel that sunk in the seas off sparsely populated Stewart Island, which is about 30 kilometers (19 miles) from the New Zealand mainland.
Easy Rider is believed to have gone down in the early hours of Thursday morning but was not reported missing until after 2 p.m. that afternoon, said Inspector Lane Todd, the area commander for the New Zealand police.
The survivor was found "clinging to a small barrel" in the Foveaux Strait around 6 p.m. Thursday, Todd said in a video interview posted on the website of the New Zealand Herald.
The man was suffering from hypothermia and has been hospitalized, Todd said, adding that his life was not in danger.
The survivor told the police that Easy Rider had capsized after being struck by a "rogue wave," Todd said.
Rogue waves "are generally considered to be unexpectedly high waves which in some instances come from a direction different from the predominant waves in the local area," according to the Ocean Prediction Center of the National Weather Service in the United States.
As of late Friday afternoon, four bodies had been recovered by a search and rescue effort involving boats, helicopters and people combing the nearby shore, the police said in a statement.
The wreckage of Easy Rider was found Friday about two kilometers off the coast of Steward Island.
"Debris has continued to surface in the vicinity of the boat's wreckage," the police said.
Specialist diving squads from Wellington, the capital of New Zealand, were expected to arrive in the region Friday evening with the equipment necessary for a deep sea dive, according to the police statement.
All nine people aboard Easy Rider were from the local area, Todd said.