The search has resumed for a missing diver in Otago and a missing teenager swept away in a Wellington river.

A police spokeswoman confirmed police would be searching again today.

A free diver failed to surface near Gull Rocks at Sandfly Bay on the Otago Peninsula on Friday evening.

The alarm was raised just before 7pm.

Advertisement

A Police dive squad are on their way from Wellington to assist in the operation and a land search will occur at low tide around 4pm.

A 19-year-old man is missing after him and his friend went for a night time swim in the Hutt River on Thursday night. The river was swollen and fast moving due to the rain.

A drone was deployed to look for the teen and police searched the mouth of the river, Wellington Harbour and the riverbanks.

The area where they were swimming is not typically a popular spot as it is very deep, wide and the currents can be unpredictable, Sergeant Anthony Harmer said.

Greater Wellington Regional Council river ranger Travis Moody said the river was at its peak when the youth entered the water.

"It gets quite ferocious, even in a smaller rain event like that. Any time the river's up you don't want to get in the water.

"It's a raging torrent basically. You'll have big boulders underneath the water moving along with that flow."

Moody said the man would have struggled to keep his head above water in those conditions.

"Even if you did get to the side, you'd have to deal with a whole lot of vegetation.

"It's pretty easy to get pulled under when it's like that, poor guy."

Police established that the two young men spoke to a man and woman in the Belmont Domain area at some stage last night and ask the couple to call Police on 04 381 2000.

If anyone else spoke to two young men in the Belmont Domain area, Police also ask for them to come forward.