PHUKET: A police investigation is beginning today into the sinking of a dive boat and the stranding of more than 400 tourists - many of them from Phuket - on an island off the Andaman coast.

Rescued safely by a Royal Thai Navy patrol boat and returned to the mainland in darkness at 3am today, the tourists were all glad to be back on shore.

But questions are likely to be asked about why the ''captains'' of more than 10 day-trip speedboats ignored official and widely-publicised forecasts of severe weather and put to sea yesterday.

The police probe will be headed by Superintendent Colonel Weerasin Kawnseng from Kuraburi in Phang Nga. The fishing port is designated as being responsible for incidents connected with Tachai island, where the stranded passengers were all taken during the storm.

The dive boat, Phuket-owned but leased to Khao Lak Scuba Adventures, sank in 20 minutes after being gradually swamped just 1.6 miles from Tachai island.

Twenty divers, five instructors and six crew were on board, according to an account of the sinking provided by an insider who wishes to remain anonymous.

The captain and an engineer stayed on the sinking two-floor vessel, the Jaoying (Little Princess), while everyone else jumped free into the water about 2.30pm yesterday.

As the boat sank, according to the insider, the captain went higher up the vessel and was eventually able to free one of two liferafts.

Two flares were fired and a fishing boat plucked everyone safely from the water after 30 minutes.

The vessel - similar in its two-storey configuration to a live-aboard named Dive Asia that went down off Phuket with the loss of seven lives in 2009 - sank in 70 metres of water.

As with the Dive Asia, any insurance claim for the 15-million baht vessel is likely to hinge on the outcome of the police investigation. Passports and belongings went down with the boat.

The passengers and crew plucked from the Jaoying were taken to Tachai island where they joined hundreds of speedboat day-trip passengers and some other dive boat guests and crew, stranded by the forecast storm.

Late last night the Royal Thai Navy vessel Pattani picked up all the tourists and crews and brought them back to Tablamu Navy Base, north of Phuket, where the ship docked about 3am.

Colonel Weerasin told Phuketwan at Tablamu early today that his investigation would begin with questioning of the passengers and crew of the Jaoying today, at the resort in Khao Lak where the guests - mostly from Europe - were all staying.

All rescued tourists were ferried early today to their accommodation in Khao Lak or on Phuket by a fleet of mini-vans.

American Sean Chapman, 36, from Bangkok where he lives and works, said early today that he was on another dive boat for three days.

''Last night we were informed that we needed to be evacuated by the military,'' he said. ''There was a storm coming in.

''So about 8pm we got onto an island and then waited for other passengers on other boats to evacuate and join us.

''The boat next to ours actually sank. I was on the Scuba Net boat. It was the first time I'd had an experience like this.

''I just came down to stay on the boat for Songkran. If not for the Navy I think we would have had to stay out there [on Tachai island] for another three or four days.

''The storm was so strong the dive boats couldn't ride through it. Without the military helping us, we would have stayed there.''