PHUKET: A huge haul of marijuana discovered in a secret underground room on Phuket had been trucked to the island from the northern city of Chiang Mai, police said today.

The street value of the 400 kilos of ''pot,'' bought for 20,000 baht a kilo, was double that when sold on, giving the large stash a total value of 16 million baht, according to the man arrested over the haul.

The marijuana may have been destined for transshipment by boat to another country, Phuket Police Commander, Major General Pekad Tantipong, told a Phuket City police headquarters media conference today that drew the interest of Phuket's Governor, Tri Augkaradacha.

While the quality of the stash has yet to be confirmed by forensic police, the label ''Angel'' indicates a top Chiang Mai marijuana brand.

Major General Pekad said police figured the marijuana was to be shipped somewhere else because Phuket drug users mostly favored methamphetamines ya bah and ya ice, not marijuana.

Samui was considered to be more marijuana territory, the major general said.

Police arrested one man, Sompong Kamutok, 23, about 10.30am yesterday after he fled a ''sting'' in a southern-Phuket Tesco store and was apprehended soon after on a motorcycle at a checkpoint near Chalong Circle.

At a house in Moo 4, Rawai, police found the 400-kilo haul in a secret underground room. Police say they are looking for three other suspects in the case.

It is not clear at this stage how the truckload of marijuana managed to evade detection at the Tachatchai police checkpoint, in Phuket's north, where all traffic coming onto and leaving Phuket is scrutinised.