The body of a Frenchman missing since he and a Spanish woman companion already confirmed drowned went swimming in the stormy sea at Koh Chang's Lonely Beach on Sunday morning was found on Monday morning.

The Frenchman was identified only as Ramkurran, 22, and the Spanish woman as Clara Crospo Canellas, 21.

A local village chief said that at about 7am he was alerted by local residents that two tourists had entered the sea off Lonely Beach in a strong storm with high waves.

The two tourists had yet to be identified.

He said a red flag had been erected at the beach, warning tourists not to go swimming in stormy seas.

The Koh Chang safety centre mobilised a number of rescue volunteers and local administrative officials to form a search and rescue team.

Team members used jet skis to look for the two tourists in an area about 300 metres from the shore, the village chief said.

The woman was found drowned in the sea about 8.10am, about 300 metres to the south, and brought ashore. The search was called off about 11am because of the bad weather.

When the search resumed on Monday morning about 20 rescuers entered the sea from the beach and combed the area, about 40 metres from the shore. They found the body of the missing man at 9.45am.

The two tourists had stayed at Nature Beach Resort Hotel for three days. On Sunday morning, they told hotel staff that they would go out to watch the sun rise, the village chief said.

The area is currently being hit by rain and high waves. Tourists should be careful before entering the sea, especially where a warning red flag has been put up, officials said.