Thailand issued an evacuation order on Wednesday for its Andaman coast, a magnet for foreign tourists, after a massive earthquake off Indonesia triggered a tsunami alert.
Thailand's National Disaster Warning Centre advised people in the area to move to higher places and stay as far away as possible from the sea.
"All people along the Andaman coast must evacuate to safe areas. We expect a tsunami 1.6 to 2.0 metres high to hit Phuket and Phang Nga at 5:40 pm (1040 GMT)," the centre's director Somsak Khaosuwan said on Thai television.
The Andaman Coast was battered by an Indian Ocean tsunami in 2004 that killed an estimated 5,400 people in Thailand alone.
Since then, Thailand has installed a high-tech warning system designed to reassure tourists and businesses that the country's beaches are safe.
The latest Thai alert, triggered by an 8.7-magnitude quake off Sumatra island, covers six southern Andaman coastal provinces.
Flights to Phuket were diverted to other airports as passengers and staff were evacuated to higher ground, officials said.
The tremor was felt as far afield as Thailand and southern India.