After getting a tipoff, police and soldiers were waiting for the traffickers at a checkpoint in Ban Loei Wangsai of Wangsai sub-district in Phu Luang district early Tuesday.
A black Honda Civic car registered in Surat Thani province arrived about 3am. It was stopped for a search as it matched the informant's information.
Police found the heroin a cardboard box they chose for a random search. The male driver then accelerated the vehicle away from the checkpoint, with the female passenger and several other boxes inside the cab.
About 9am authorities found the car abandoned in Ban Non Pattana in the same sub-district. Then they found the man and the woman at a viewpoint on the road in Ban Huai That.
They were identified as Nathabun Burirat, 43 from Surat Thani, and On-anong Kaeokhao, 33 from Nakhon Pathom. They admitted to transporting the heroin in the car and to dumping six other boxes from the viewpoint.
The boxes seized from the suspects contained a total of 127kg of heroin, worth about 210 million baht locally and in excess of one billion baht if smuggled out of Thailand.
Officials also found 40,000 methamphetamine pills in their car.
Deputy police chief Pol Gen Pongsapat Pongcharoen said narcotics suppression police were investigating to determine the source and destination of the heroin. Initial information indicated the drugs came from a neighbouring country and were smuggled into Loei.
The heroin was probably en route to the South and then to traffickers in Malaysia, or intended to be hidden in seafood packages destined for Australia, Pol Gen Pongsapat said.