Thai police arrested 15 members of a Malaysian drug gang which was trying to smuggle millions of dollars worth of crystal methamphetamine and heroin to Malaysia.

Thai police were acting on a tip-off that couriers were attempting to smuggle a huge stash of drugs in a train travelling from northern Thailand to the Malaysian town of Butterworth.

"This gang chose to transport drugs by train rather than by car because transporting by car is riskier as there are several checkpoints," Lt-Gen Thitiraj Nhongharnpitak tol the Bangkok Post.

The consignment included 226 kilograms of crystal meth and 8 kilograms of heroin. The meth is worth an estimated 452 million baht ($13 million), the police said.

The drug's street value in Malaysia would be almost double this amount.

Thai railway police detained two smugglers on Wednesday who were allegedly carrying 23 kilogrammes of crystal meth.

Police conducted raids based on the leads gained from them, leading to one of the biggest drug hauls in the country.

12 more suspects were arrested and a bigger drug consignment was discovered in subsequent raids on a South-bound express train from Bangkok to Butterworth.

The smugglers went by ethnic Malay and Chinese names, Thai police said.

Northern Thailand is an important part of the so-called Golden Triangle, through which most of the drugs manufactured in Myanmar passes through.