Seven people were rescued from the water off Kaikoura after their fishing charter boat sank this morning.
Kaikoura Coastguard president John Macphail said a mayday call was picked up on radio about 9.40am but there were no other details and all they knew was that someone might be in trouble.
''We took it seriously but had nothing to go on,''' he said.
Maritime New Zealand put out a call out and a long-line fishing boat responded that it was picking people out of the water.
''It was a very good result in the end,'' Mr Macphail said.
He believed the stricken boat started taking on water because of an equipment failure, but he was unsure what had happened for it to sink so quickly.
A private fishing boat was also involved in the rescue, picking up five of the people from the charter boat.
The boats were off the coast in an area known as Shark's Tooth.
Constable Tony Willetts, of Kaikoura police, said the party of six were all from the Oxford area, near Christchurch.
All of them were treated by ambulance staff after they had been rescued but were all fine, he said.
He had no idea what had caused the boat to sink, but it would be investigated by Maritime New Zealand.
Everyone had been wearing a lifejacket and they all got back to shore safely, he said.