A body has been found near a popular Northland Beach early this morning, shocking locals of the tight-knit Mangawhai community.

A witness has told the Herald he was awoken to the sound of a fire siren at 6.30am, and soon after received a call from a friend to say the Mangawhai estuary between two boat ramps had been cordoned off by police.

"The whole community woke up after the siren."

He went down there himself to find police erecting a tent.

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Police confirmed they were called to reports of a sudden death on Mangawhai Beach this morning.

Police enquiries were ongoing and the death would be referred to the coroner.

The body had since been moved but a cordon was in place this morning as local fire officers kept the public away, Mangawhai fire chief Robert Leslie said.

The Herald understands a member of the public came across the body about 6.20am, before the fire siren sounded 10 minutes later.

The person who found the body was confident the body was that of a woman in her 30s who had been swimming last night.

The Herald understands that the woman had consumed alcohol and people were out looking for her last night.

RnR Charters Ltd director Stef Railey said she had been contacted by the witness early this morning as they feared the body was that of her partner given the scene's proximity to their own moored boat.

The body was about 100m from where they moored their boat used for charters but thankfully her partner was safe, she said.

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The harbour was a popular spot for swimming but was dangerous for those who were uninitiated.

"People swim in the harbour and there is quite a strong flow, and some big tides at the moment. It's a trap for new players.

"They get out there and can't come back in."

People swam right across the estuary and people frequently used the current to carry them so they didn't have to swim. The current was about 3 knots strong.

Police would have to conduct their scene examination quickly as the body would need to be moved before low-tide around midday, Railey said.