More than 300 people have died and 3,500 were injured after the massive sea surges caused by an earthquake smashed into Thailand's western coast.
The tourist resort of Phuket was devastated
The worst hit areas were on beaches near Phuket, with reports of divers and sunbathers being swept out to sea.
Hotels were under water after 5m-10m (16 to 33 feet) waves hit the coast and there were reports of tourist bungalows being carried away by the water.
Tourists spoke of their disbelief at the scale and speed of the disaster.
"The beach is a disaster now with all of the local restaurants and beach chairs businesses totally destroyed," one reader in Phuket told the BBC News website.
One hotel worker in Phuket said the tide of water flooded the hotel lobby and pulled furniture onto the street.
"As I was standing there, a car actually floated into the
lobby and overturned because the current was so strong," Boree Carlsson told Reuters news agency.
There were particular fears for divers, since the tidal wave hit when hundreds of tourists and instructors were in the water for a Boxing Day dive.
Around 80 divers were reportedly rescued from the famous Emerald Cave, which divers can only reach by swimming underwater. Another two are said to have died.
On the island of Koh Phi Phi, made famous as the location for Hollywood film The Beach, officials spoke of widespread damage and islanders and tourists being airlifted to safety.
One report from the island said 200 bungalows had been swept out to sea.
Tourism is one of Thailand's most important industries, with hundreds of thousands of tourists drawn to its beaches each year.
In neighbouring Malaysia, at least 42 people were reported killed after the tidal waves hit. Most of the dead were in the holiday resort of Penang.