Searchers have failed to find a man lost overboard in Endeavour Inlet in Queen Charlotte Sound.
Police say the Marlborough man, 35, is believed to have fallen from the 14m private launch about 2am on Tuesday.
Officers say the man was not wearing a lifejacket.
The boat had left Furneaux Lodge and was motoring towards Punga Cove at the time of the incident.
Police, the Coastguard, a helicopter and the Cook Strait ferry Straitsman have all been involved in the search.
The police dive squad came from Wellington on the police launch Lady Elizabeth lV to help.
Police are also interviewing people who were on the launch and people who had contact with the missing man before the incident.