The police dive squad arrived about 11am, first searching the area Mr Tapu had last been seen, then carrying out a systematic grid search of the wider area.
"He's an experienced diver, he's been diving here for the last four to five days without incident, and he was in three to five metres of water 50 metres offshore, so it's a real mystery what's happened," Senior Sergeant Metcalfe said.
The summer had already seen an exceptional number of drownings, many of which could have been avoided with simple precautions, he added.
"The fine weather means large numbers of people are on the water, but they're making the same basic mistakes, and paying for it with their lives," he said.
He urged swimmers to be aware of powerful rips on the west coast and boaties to always wear a life jacket and let someone know where they were going. Divers should not dive alone, or have someone watching all the time, and young children needed to be watched constantly.
"Take your eyes off them for a moment and they're gone," he said.
Meanwhile Parapara man Aaron Rewa Inch said he saw Mr Tapu standing on a rock while others on the beach called for him to come back. He sat down on the rocks then disappeared into the water and did not resurface.
"He didn't look right. He looked groggy," Mr Inch said, adding that a boat had been launched to begin searching within a matter of minutes.
