Three people, including a child, survived floating in the ocean for 16 hours in the ocean off Tasmania after their boat sank last night.

But one man remains missing, with police boats and helicopters still searching the waters near Robbins Island.

The four people are thought to have been staying at Montagu campground in the state’s north-west when they set off for a fishing trip at around 5.30pm last night.

Tasmania Police confirmed the Westpac Rescue Helicopter is involved in the search for the missing boat. (Sitthixay Ditthavong)

They failed to return, with concerned relatives raising the alarm with police at about 8am this morning.

The Westpac Rescue Helicopter was dispatched and about 1pm, two adults and a child were found floating in the water at Robbins passage.

Police believe the boat they were in broke up at about 9pm last night, with all four to be thrown into the water.

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They were not rescued for around 16 hours.

They were taken to North West Regional Hospital due to the amount of time they spent in the water, but police say they are otherwise uninjured.

The trio were wearing life jackets.

Tasmania Police said in a statement several boats, as well as the Westpac Rescue Helicopter, were deployed in the search.