Laos police have made their second-biggest single seizure of illegal drugs, uncovering 36 million methamphetamine pills, a United Nations official said Saturday.

The raid in the northern province of Bokeo came three months after officers netted Asia's biggest ever haul in the same area with 55 million meth pills found in a beer truck.

Laos is part of the Golden Triangle covering the border areas with Myanmar and Thailand that has for decades been a hub for Southeast Asia's lucrative drug trade.

Since Bangkok ramped up border patrols to stop the spread of coronavirus, Laos has become a gateway for traffickers moving meth out of Myanmar's troubled Shan state across the Mekong River into Thailand.

UN Office on Drugs and Crime regional representative Jeremy Douglas said four people were arrested in connection with the drug bust in the town of Huay Xai on Wednesday and authorities also found 590 kilograms of crystal meth.

"Those four who were arrested were pretty low level... there were no kingpins," he told AFP.

Photos seen by AFP show the suspects and police in front of a wall of drugs -- sacks piled up like sandbags.

"It's the second-biggest seizure Laos has ever made. Thailand has never made a seizure that size," Douglas said.

Thai media reported that heroin and a shotgun were also found during the night raid.

The meth tablets were believed to be destined for Thailand but the ice was intended for higher value markets including Australia, Douglas added.

The glut of meth pills in the region has sent street prices plummeting in Bangkok and other Southeast Asian cities.

Experts say methamphetamine production is at unprecedented levels and has been exacerbated by the coup in Myanmar a year ago that paralysed the economy and livelihoods.

Myanmar's lawlessness is providing ideal conditions for illicit drug labs to flourish, with a largely unchecked supply of precursor chemicals flooding in from China.