Rescue teams believe that a missing British woman is trapped inside a sunken ship 180ft below the sea surface off the coast of Thailand.

Navy officials said that Millie Young, 57, was dragged down in the choppy waters as 12 other holidaymakers fled the vessel when it sank four miles from the Surin Islands archipelago on December 23.

The ship's cook Samniang Chaichana, 67, is also thought to have drowned with Millie, who was on the diving and snorkelling trip with the Degregorio family, also from Brighton.

Navy chiefs said they will now use sonar to find the wreckage of the Reggae Queen, a large liveaboard ship that took tourists on overnight diving trips around the idyllic tropical islands, some 37 miles from the mainland in Phang Nga province.

Pichet Songtan, spokesman for Thai Maritime Enforcement Command Centre (Thai-MECC) Region 3, said: 'The rescue committee is working to find the sunken ship as quickly as possible. We believe that the missing people are trapped inside.

'The captain of the tour boat has provided additional information. He said that the boat had left Thap Lamu Pier in the afternoon of December 22, along with 13 tourists and five boat crew members.

'On their way to the target dive point at Ko Torinla island, the waves were so strong, so he stopped the boat at anchor at Ko Phra Thong to wait for the wind and waves to calm down.

'When the wind and waves calmed down, they continued sailing towards the destination but it turned out there was a strong wind near the destination as well.

'At around 4 am, the waves were more than three meters high, then the water began to wash into the boat.

'The waste water pump in the boat could not remove the waste water. Therefore, the ship's officers were asked to wake up all the sleeping tourists, along with arranging life rafts for evacuation before the ship sank.

'The ship floated on the waves for more than three hours until another boat found it and rescued the group at around 9 am.'

The rescue chief said that a 'side-scan sonar' had been requested from the navy's battle fleet to find the co-ordinates where the ship sank.

While tracking the wreckage has been made more difficult by the strong wind and currents at the time of the sinking.

He said the severe weather and the depth of the ocean, around 55 meters (180ft) in that region had so far prevented divers from exploring the seabed.

The navy chief added: 'The rescue committee consists of 3rd Naval Area Command, Thai-MECC Region 3, and the Surin Islands National Park.

'The mission plan consists searching on the surface, on the beach, and from aircraft, and requesting cooperation from nearby vessels.

'The missing persons are likely to be stuck inside the ship. We believe that they were unable to escape and were pushed down by the water.

'We are still waiting for the correct latitude and longitude to be determined. When it is, deep sea scuba divers are ready to search further.'