Nong Khai celebrates the generic Thai and Isaan festivals with due gusto, but in recent years a peculiarity of this stretch of the Mekong River has been attracting thousands of celebrants from Bangkok and beyond. Every year on the full-moon night in October, silent and vapourless naga fireballs appear from the river, small, pink spheres that float vertically up to heights of as much as 300m, then disappear; in some years, several thousand appear, in others, just a handful. A tentative scientific theory proposes that the balls are a combination of methane and nitrogen from decomposed matter on the bottom of the river, which reach a certain temperature at that time of the year and are released, combusting in the presence of oxygen when they break the water’s surface; romantics will prefer the local belief that the nagas or naks (serpents) of the river breathe out the fireballs to call the Buddha to return to earth at the end of Buddhist Lent.

This strange occurrence has now been consolidated into the two-day festival of Bang Fai Phaya Nak, which coincides with Awk Phansa and the end of the longboat-racing season on the river. The fireballs have appeared as far afield as Sang Khom and Bung Kan, but are generally most numerous at Phon Phisai, 40km east of Nong Khai; if you make the trek out there, take great care on the way back, when the road is thronged with drunk drivers.

Book through Rough Guides’ trusted travel partners

Thailand features

The latest articles, galleries, quizzes and videos.

Video: a 1 minute guide to Thailand

Video: a 1 minute guide to Thailand

Whether you're planning a two-week holiday or an epic backpacking trip, Thailand remains one of our readers' favourite destinations, and with good reason. Th…

01 Nov 2017 • Colt St. George videocam Video
Budget trips: 20 of the cheapest places to travel

Budget trips: 20 of the cheapest places to travel

That ever-growing travel wish list might be putting some pressure on your pocket – but there are plenty of destinations where you'll get more bang for your b…

11 Oct 2017 • Emma Gibbs camera_alt Gallery
Go it alone: solo travel in Thailand

Go it alone: solo travel in Thailand

Thailand is the quintessential backpacker destination. Here you can make the first footprints on secluded sands, dance shoeless under a full moon and swim benea…

28 Sep 2017 • Helen Ochyra insert_drive_file Article
View more featureschevron_right

Weekly newsletter

Sign up now for travel inspiration, discounts and competitions

Sign up now and get 20% off any ebook