BANGKOK (AFP) - Thailand's water-soaked new year festival Songkran kicked off on Wednesday (April 13), as the authorities geared up to scrub the party clean of alcohol, topless dancers and other "indecencies".

The three-day festival is traditionally celebrated by paying respect to elders and visiting temples to sprinkle water over Buddha figures.

But the holiday, which takes place at the peak of Thailand's sweltering dry season, is also known as one of the world's biggest water fights, with crowds of revellers battling in the streets and dousing passers-by.

Merrymakers this year are bracing not only for the sudden splashes of water that can come from any direction, but also threats from the authorities to arrest scantily clad women and ban alcohol from the raucous street bashes in an effort to return the festival to its traditional roots.

"It is also essential that we maintain our cultural heritage through genuine traditional activities, such as pouring water on Buddha statues," the country's Prime Minister Prayut Chan-O-Cha said in his weekly televised address ahead of the holiday week.

"There are laws governing indecent exposure, which will be enforced. You should celebrate in a polite way as there will be people of all ages joining in," added the junta chief, whose administration has launched a streak of public morality campaigns since seizing power in a 2014 coup.

Police in recent days have warned that they will block the trucks carrying topless dancers - both women and transgenders - that have become a common feature of Songkran street parties.

The authorities have also urged revellers to spray water more sparingly this year, as the country is currently in the grip of the worst drought in decades.

The severe water shortage has forced many rice farmers to cut back on planting this season and seen some villages deprived of tap water.

In neighbouring Myanmar, one of several other Buddhist countries in the region to also celebrate the festival, the authorities have similarly warned against wasteful water usage and called for a return to traditional celebrations.