Thai authorities intercepted a tonne of crystal methamphetamine in one of the kingdom's biggest ever single seizures of the illegal drug, police said Sunday.

The haul, with an estimated value of more than US$25 million on the international market, was found when officers stopped a pickup truck in central Nakhon Nayok province on Friday.

Acting National Police Chief Kittharath Punpetch said police, military and local officials had been monitoring several smuggling gangs and learned of a plan to move a large amount of the drug, commonly known by the street name "ice".

Kittharath told a news conference that 40 bags of the drug, weighing a tonne in total, were found in the truck.

Its driver was arrested but investigators believe the head of the smuggling network is a Thai national based in a neighbouring country.

The kingdom is a major transit route for illicit drugs produced in the so-called "Golden Triangle" region where northern Thailand, Laos and Myanmar meet.

Myanmar is a major source of amphetamine, much of it produced in illegal labs in border areas controlled by ethnic minority armed groups. (AFP)