Police say a young man who jumped off a wharf in Devonport in Auckland and did not re-surface is unlikely to be found alive.
Three witnesses saw the man strip naked and jump into the water just before 8am today.
Police said an extensive search had so far failed to find the 18-year-old, whose identity is known.
A spokesperson said the police helicopter, harbourmaster, the police launch and two smaller boats all scoured the water for about an hour and a half with no luck.
He said the situation was looking grim and the police dive squad was travelling up from Wellington.