A South Korean fishing boat sank on Monday in freezing waters near Antarctica and five members of the crew were killed and 17 missing, New Zealand and South Korean authorities said.

Twenty members of the crew of the 614-tonne, 58 metre (190  foot) toothfish boat No 1 InSung had been rescued by a ship.

The boat sank at 6.30 a.m. (1730 GMT) about 1,850 km  (1,150 miles) north of Antarctica and 2,700 km (1,700 miles)  south of New Zealand, the country's Rescue Coordination Centre  said.

It was not known what caused the ship to sink and no distress call had been made, the centre said.

Information from the ship carrying the survivors suggested the boat sank quickly, giving crew no time to put on life  jackets or immersion suits, the centre said.

The search has been scaled back with three South Korean vessels looking for the missing men. Two New Zealand vessels have stopped searching and an aircraft would not be sent.

"Unfortunately, given the short survival times in water of those temperatures and the length of time it would take for the ... aircraft to reach the search area, it was not a viable  option," said New Zealand rescue centre controller Dave Wilson.

The water temperature is about 2 Celsius (35 Fahrenheit) which means someone would survive for about 10 minutes without proper equipment, the centre said. – Reuters