Survivors managed to alert the authorities to their police
Fifty-four Burmese migrants have been found dead after suffocating in a lorry smuggling them into southern Thailand.
More than 100 people were packed into a container measuring 6m by 2m. Many of the survivors are seriously ill from dehydration and lack of oxygen.
The driver opened the doors of the vehicle after the migrants banged on the walls - but he fled on foot when he saw what had happened.
Thousands of Burmese risk the trip to Thailand in the hope of better wages.
Police said the Burmese had crossed by boat to the Thai town of Ranong from Burma's southern tip at Victoria Point - a route often used by illegal migrants.
They had then been packed into an airtight container on a lorry for the journey to the resort island of Phuket.
Local police chief Col Kraithong Chanthongbai said the ventilation in the container had failed.
"The [survivors] 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 the French news agency AFP.
Thailand: 141,000 refugees in camps, about 500,000 registered migrants, up to 1,350,000 unregistered
Bangladesh: 27,000 refugees in camps, 200,000 unregistered
Malaysia: 30,000 refugees, several thousand unregistered
India and China: Tens of thousands of unregistered workers in border states of Mizoram and Yunnan respectively
Sources: UNHCR, NGOs
Police said at least 47 migrants survived and 54 died - 37 women and 17 men.
The survivors who did not need hospital treatment were detained by the Thai authorities.
Saw Win, a 30-year-old survivor, told the Associated Press from police custody how he believed everyone would perish in the lorry.
"I thought everyone was going to die. I thought I was going to die. If the truck had driven for 30 minutes more, I would have died for sure," he said.
It is thought the migrants paid between 5,000 baht ($155; £75) and 10,000 baht for their passage into Thailand.
There are thought to be up to two million Burmese workers in Thailand, more than half of whom are in the country illegally.
They fill the low-paid, often dangerous jobs in sectors including textiles, construction and fisheries that Thai workers do not want.
But these jobs offer the migrants salaries that far exceed what they could earn in military-ruled Burma, one of South East Asia's most impoverished nations.