(CNN) -- A South Korean fishing vessel sank Monday in frigid ocean waters about 1,000 nautical miles north of McMurdo Station in Antarctica, killing at least four people, while at least 20 were rescued, according to maritime officials.

A time-sensitive search was underway for another 17 people who were missing, said Maritime New Zealand spokesman Ross Henderson. While the ship sank in the Southern Hemisphere's late spring, water temperatures are just 2 degrees Celsius (35.6 degrees Fahrenheit), meaning crew members likely could only survive no more than 10 minutes before succumbing to hypothermia, authorities said.

There were differing numbers on the size and fate of the crew.

The New Zealand federal agency, which focuses on ocean-based search, rescue, safety and environmental matters, said that five people had died, 20 were rescued and 17 were missing.

But Ham Un-Shik, a spokesman with the Busan Coast Guard in South Korea, said four people were dead, 21 had been rescued, and 18 were still missing.

The 58-meter (190-foot) fishing trawler, the No. 1 Insung, left on November 2 from South Korea to fish in Antarctic waters, said Ham. It had 11 Indonesians, 11 Vietnamese, eight Koreans, eight Chinese, three Filipinos and one Russian on board, he said.

The ship sank about 6:30 a.m. (12:30 p.m. ET Sunday) in a remote swatch of the Antarctic Ocean some 1850 kilometers (1150 miles) north of McMurdo, a U.S. research center on the tip of Ross Island, according to Henderson. Maritime New Zealand learned of the incident around 1 p.m., some four-and-a-half hours later.

There was no emergency radio call before the incident, and it is still not clear what happened, Henderson said.

Two New Zealand fishing vessels nearby were at the scene, with three South Korean trawlers closing in to lend assistance, Henderson said from Wellington, New Zealand. Authorities called on all other nearby ships likewise to go to the area to help.

The seas in the area were relatively calm, with 1 meter (about 3 feet) high swells and a light westerly wind, added Henderson.