Police have seized 508 kilogrammes of crystal methamphetamine or "ya ice" with a street value of more than 1 billion baht.
Police led by national police chief Chakthip Chanijinda announced the seizure of the drugs at a briefing Tuesday.
Pol Gen Chakthip said police in Nakhon Ratchasima's Sida district set up checkpoints early on Monday after being tipped off that drugs would be transported via routes in the district.
A pickup truck emerged near a police checkpoint but made a U-turn apparently to flee police, prompting a chase by authorities. The vehicle managed to escape at the time.
By 12.50pm, police were alerted by local people that the pickup truck had been left near a temple in Bua Yai district of Nakhon Ratchasima. A search found 508 packets of crystal methamphetamine, weighing one kilogramme each, hidden in the back of the vehicle.
After checking footage from close-circuit television systems, police later arrested a man identified as Tinnakorn Khomsingh, a 30-year-old native of Nakhon Phanom, at a Bua Yai railway station.
He allegedly told police that a member of a drug gang paid him and the other man, identified only as Bee, 20,000 baht each to transport the drugs from Nakhon Phanom, though it was not revealed to him where the drugs were headed.
His employer only called him on the phone to tell him the routes he had to use -- Sakhon Nakhon, Kalasin, Maha Sarakham, Khon Kaen's Ban Phai and Phon districts and Nakhon Ratchasima's Sida district.
Police are looking for the other suspect who is still at large, and will expand the investigation to arrest the mastermind.
Pol Gen Chalermkiart Srivorakhan, deputy national police chief, said transit routes for drug smuggling had changed from the North to the Northeast following tougher police measures to stem the influx along the northern border.
The seized drugs were believed to be destined for Malaysia via the South before being distributed to other countries.
In another development, police seized 14,460 pills of methamphetamines and 25.4 grammes of ice in Kantharalak district of Si Sa Ket and arrested four people.
