Specialist police divers are joining the search for a man who's missing in the Marlborough Sounds.

The 25-year-old had been free diving off Titi Island, before police were alerted to his disappearance yesterday afternoon.

Search and rescue teams, the Coastguard, a helicopter and private vessels all scoured the area.

The search is resuming Wednesday, with the police dive team from Wellington joining efforts along with the police maritime unit.