A Buddhist monk has been arrested in Burma after authorities said they found more than four million methamphetamine pills in his car and his monastery.

The monk was stopped as he drove in northern Rakhine state, which borders Bangladesh, said police officer Maung Maung Yin. Authorities had been tipped off that the monk was carrying an illegal haul.

​Maung Maung Yin said an anti-drug task force found 400,000 pills in the monk's car. A subsequent search of his monastery turned up 4.2 million pills along with a grenade and ammunition.

Burma is a major producer of methamphetamine, usually smuggled from the north-east to neighbouring countries. It is also the world's second biggest producer of opium, from which heroin is derived.

"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, the director general of the religious affairs ministry, Soe Min Tun, acknowledged some surprise. "It is not a very common case, but not impossible to happen. 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," he said.

Police said they were still questioning the monk.

Last year, Burma officials seized 21 million methamphetamine pills with a street value of around $35.5m (£28.7m) near the border with China, in the biggest such seizure in recent memory.