BANGKOK, Oct 21: Security measures at this year’s mysterious fireball festival at the Mekong river have been significantly increased the Tourism Authority of Thailand (TAT) said on Monday.

“We expect at least 200,000 tourists to come and see the event (Monday night),” Nual Sarnsorn, director of TAT’s office in Udon Thani, 450 kilometres northeast of Bangkok, told dpa.

“Everybody, the TAT, the police, and the provincial authorities, are concerned about security for the tourist, because of the terrorist attack in Bali a week ago.”

Every year, small and bright fireballs shoot up quietly from the Mekong river at Nong Khai, 490 kilometres northeast of Bangkok.

The phenomenon which is still scientifically unexplained is called “Bang Fai Phraya Nark” or “Naga’s Fireballs” and usually happens on the first full-moon night of October coinciding with the end of Buddhist Lent.

Local people believe the fireballs come from a mystical Naga or serpent living in the Mekong river who is spitting them high up in the air.

Scientist, however, assume the fireballs might be caused by bubbles coming up from a combustible natural gas deposit in the river bed which ignite when shooting up.—dpa