Chalong Police reported that the dive tour boat "Phoenix Diving" overturned near Koh Hei, south of Phuket, at about 5:45pm with a reported 97 people on board.
"Tourists are floating in the sea," confirmed the report.
Another tour boat, named by police in Thai as "เซเน็ตต้า" (phonetically resembling "Zanetta")**, with a reported 39 people on board overturned near Koh Mai Thon, southeast from Phuket.
The police report noted that the boat had sunk.
Emergency services have been scrambled. However, at last report that the rescue teams were finding it difficult to carry out the rescue with darkness falling and the strong wind and waves continuing.
All available ambulances in the area have been ordered to stand by at Chalong Pier.
The Royal Thai Navy has deployed rescue vessels from the Third Area Command at Cape Panwa, on Phuket's east coast, the report added.
Tourist Police, Marine Police and a vessel from the "Kai Mook Centre" were also been deployed to render assistance.
At the time of the report no deaths or injuries had been reported to police, the report noted.
Police also included in their initial report an incident involving two Russians who were riding jet-skisnear Koh Racha late this afternoon.
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** Later confirmed by the actual name painted on the hull as the "Serenata".