BANGKOK - At least 54 Myanmar migrant workers suffocated to death as they were being smuggled into Thailand inside a cold storage container, police said Thursday.

The victims were among 121 people crammed inside a container that was six metres (20 feet) long and only 2.2 metres (seven feet) wide, said Colonel Kraithong Chanthongbai, commander of the local police station in the Thai border province of Ranong where the bodies were found late Wednesday.

Twenty one people also suffered from a lack of oxygen inside the container and were taken for treatment, he said.

The migrants were supposed to pay a Thai smuggling ring 5,000 baht (157 dollars) each to transport them from the Myanmar-Thai border in Ranong to the nearby resort isle of Phuket, he said.

Once there, they hoped to find work as day labourers, he said.

When the man driving the truck carrying the container realised some of the migrants had died, he parked on the side of a road, opened the door to the container, and fled the scene, Kraithong said.

"The people said they tried to bang on the walls of the container to tell the driver they were dying, but he told them to shut up as police would hear them when they crossed through checkpoints inside Thailand," he told AFP.

The bodies of the dead have been taken to a cemetery, where they will be buried in temporary graves until they can be collected by relatives, he added.

The 46 people who survived the ordeal without injury have been arrested, he said.

About 540,000 migrant workers are registered to work in Thailand, most of them from Myanmar, according to the labour ministry.

But as many as one million undocumented workers are believed to be in the kingdom, where they often face exploitation by their employers, according to rights groups.