Thai police say 56 people are still missing in waters off the resort island of Phuket after a storm capsized a diving boat packed with tourists.

The commander of Phuket Provincial Police, Teerapol Tipcharoen, says seas have calmed since the accident on Thursday evening and the search is ongoing.

The boat was carrying 105 people, including 93 tourists, 11 crew and one tour guide when it toppled in 5-metre-high seas.

One Chinese man has been confirmed dead, and at least 12 people are hospitalised.

Another boat also overturned off Phuket on Thursday. Officials said all 42 on board have been rescued.