This Friday - the first full moon of the eleventh lunar month - hundreds of red, pink and orange fireballs the size of eggs will soar up into the sky, drawing huge crowds of spectators.
The event is known as Naga's Fireballs and has been reported by locals for generations, but with no readily available scientific explanation.
Seeking an explanation
The ministry of science and technology began an investigation into the phenomenon earlier this year after a television programme claimed the fireballs were actually caused by tracer bullets fired by Laotian soldiers across the border.
But 93-year old Kohmen Phoh, the most elderly of the residents in Ban Nong Khiate where the Naga's fireball appears, said he had seen the phenomenon since he was a young boy.
“I call it the Naga's fireball in accordance with what my elders said. It happens naturally and no one stages the event."
Scientific reason delayed
Researchers led by Saksit Tridech, the deputy permanent secretary of the ministry, said that the team had studied soil and water samples from the area where the fireballs appear to originate.
They found that monsoon floods in the area triggered a complex geological process.
"When the complex biogeochemical process occurs at the appropriate time, it could cause several unusual phenomena," Saksit said in a statement, adding that another year of research would be necessary to prove his own personal theory.
“I call it the Naga's fireball in accordance with what my elders said. It happens naturally and no one stages the event"
But legend says the flames come from a mythical Naga, or serpent, living in the Mekong river.
The event has become a major tourist attraction and revenue-raiser for the region near the best viewing spot, in Phon Phisai district, 50km outside Nong Khai provincial town.
Last year more than 100,000 tourists flocked to witness the event, and several hotels in the area are booked out for Friday's event which can cause 50km traffic jams.
According to descriptions going back more than 100 years, tradition has it that a Naga living under Mekong River shoots the fireball into the air to celebrate the end of Buddhist Lent.
However, the Naga's fireball does not only takes place in the Mekong River, but also appears in the ponds and rice fields on the Laos side of the border too.
The event has enjoyed very little publicity until recent times. But now Thai officials are announcing this event through mass media including radio, TV and newspapers.
People are expected to flock to the banks of the river for three hours after sunset to watch the unexplained phenomenon this Friday.