The search will resume at first light tomorrow but rescuers said there little chance of him surviving and they were now looking for a body.
The alarm was not raised until after 9am today when the wife of one of the men called police.
Inspector Mark Hall said the men were thought to have been due home last night and it was not known why emergency services were not alerted earlier.
Mr Hall said details of what happened were not yet available.
"All we know is the boat sank about 6pm with five persons on board. Four came ashore."
There was no mayday call, and police did not yet know how quickly the boat sank.
Mr Hall said the four survivors were lucky to survive the very cold conditions.
He said the crew had the "appropriate number of lifejackets" on the boat but they were "not wearing anything smart as far as gear goes".
He said the four found on the beach were very cold.
"The chill factor would be awful."
- NZPA