Acting upon a tip-off, members of the 31st Ranger Forces Regiment of the Pha Muang Task Force and Mae Chan district police set up a road block on a road between Mae Chan and Chiang Mai's Mae Ai district.
About 1.30am on Tuesday they tried to stop a pickup truck and accompanying motorcycle, but the drivers sped off. The car was crashed into a house in Lao Fu village of tambon Pa Tueng and the two smugglers fled.
The pickup truck was found to be loaded with 25 sacks containing 4,996,000 speed pills.
Officials linked the drugs to a major smuggling syndicate operated by Lahu people.