Police in Myanmar say three Buddhist monks have been arrested after authorities found more than four million methamphetamine pills - worth about $6m - in a car and monastery.

Arsara - also known as Min Naing - was stopped on Sunday as he drove in northern Rakhine state after authorities were tipped off that he was carrying an illegal haul, Maung Maung Yin, a police officer, said on Tuesday.

Pyin Nyar Nanda - also known as Aye Lwin - and Khone Na La - also known as Thein Shwe - were the two other monks caught by police in the town of Maung Daw over links to the narcotics found.

Myanmar vigilantes take on drug lords

Maung Maung Yin said an anti-drug task force found 400,000 pills in Arsara's car.

A subsequent search of his monastery turned up 4.2 million pills along with a grenade and ammunition.

A statement from the office of the state counsellor for Myanmar's leader, Aung San Suu Kyi, said that $769 in cash was also found in the vehicle.

"This is not a normal case, and when we were informed that the monk was arrested, we were all shocked," said Kyaw Mya Win, a township police officer.

Asked about the case, Soe Min Tun, the director-general of the religious affairs ministry, expressed surprise.

"It is not a very common case, but not impossible to happen," he said.

"What will happen to the monk is that he will have to give up his monkhood right away and face trial as an ordinary person."

Major producer

Myanmar is a major producer of methamphetamine, usually smuggled from the northeast to neighbouring countries.

It is also the world's second biggest producer of opium, from which heroin is derived.

The meth pills are are hugely popular across Asia among everyone from wealthy clubbers to exhausted blue-collar employees working long shifts.

READ MORE: Drugs and bullets in Myanmar

Last year police confiscated a record 98 million stimulant tablets, nearly double the 50 million seized in 2015.

Drug prosecutions also jumped around 50 percent from 2015 to 13,500, which police said reflected the growth in the local drug trade.

Trafficking has particularly been on the rise in Rakhine state, home to more than a million people from the impoverished Muslim Rohingya minority.

In September state media reported that two men had been arrested after 6.2 million methamphetamine tablets were found in their car in Maungdaw.