A search for a man who went missing after a boat sank in the Aparima River estuary near Riverton in Southland this afternoon has suspended for the night.

The search was suspended around 7pm because it became to dark for the search to continue.

Police were made aware around 2.30pm a three-metre alloy dinghy sank in the estuary with three people on board.

Two others made it to shore unhurt, however, a third person remains unaccounted for, a police spokesperson said.

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"A search involving Coastguard, Police Search and Rescue, LandSAR volunteers, and a helicopter was suspended just after 7pm," the spokesperson said.

"It is expected to resume around first light tomorrow, which will coincide with low tide around 7am."

Metservice meteorologist Leigh Matheson told the Herald the weather for the region had been fine and partly cloudy throughout the day.

"Fairly light winds although there's a Westerly that's been picked up in the afternoon.

"About 12 to 13 degrees, pretty quiet, nothing out of the ordinary," she said.