Smokers who flout a smoking ban on 20 of Thailand's most famous tourist beaches will face a $3,000 fine or up to a year in prison, Thai authorities have said.
The ban, which comes into force in November, follows a clean-up of nearly 140,000 cigarette butts from a 2.5 kilometre (1.5 mile) stretch of the famed Patong beach in Phuket island province.
Its introduction coincides with Thailand's peak tourist season and will be enforced in visitor hotspots including Krabi, Koh Samui, Pattaya, Phuket and Phang Nga.
"These beaches are among the most beautiful in Southeast Asia, and the aim is to keep them that way," Tourism Authority of Thailand (TAT) Governor Yuthasak Supasorn said in a statement on Monday.
Smokers will have to use designated areas with proper waste disposal for cigarette butts, he added.
Those caught lighting up on the beach could face jail or a 100,000 baht ($3,000) fine, according to TAT.
The edict is the latest effort to rein in Thailand's free-wheeling tourism industry.
The sector is a crucial pillar of Thailand's economy, catering to more than 30 million travellers per year.
But the huge numbers of arrivals have also threatened to spoil some of the kingdom's idyllic beaches, with litter and unchecked development damaging local ecosystems.
Thailand is also trying to crack down on lax safety standards that riddle the tourism industry, after waves of complaints that visitors are overcharged or not adequately protected on boats and jet-skis.