Three adults and a baby were plucked safely from the waters of Wellington Harbour last night after the yacht they were on sank.

Police launched a rescue operation about 8.12pm when they were told a yacht in Evans Bay, near Point Halswell, was sinking. The yacht was reported to be an orange trailer sailor with white sail.

A member of the public told police the three people on board were in the water and the boat was drifting north.

A police central communications spokesman said a police inflatable boat, police shore units, airport marine rescue and Wellington Volunteer Coastguard were all sent to the incident. Wellington Marine Radio put out an "all ships" broadcast for any vessels in the area to assist.

Police shore units and members of public were watching the drama unfold and giving police communications centre updates on the situation.

About 8.25 pm three adults and a baby were plucked from the water by the yacht Marishka that was returning to Evans Bay.

Police came alongside the yacht and transferred the baby and mother to their vessel before taking them to Evans Bay marina for medical attention by ambulance crew. The other two adults were returned to Evans Bay on the yacht and also transferred to Wellington Hospital and treated for hypothermia.

Wellington Volunteer Coastguard recovered the sunken yacht and towed it into Evans Bay boat ramp.

All occupants of the yacht were believed to be in a stable condition in Wellington Hospital.