An additional 47 workers survived the incident late Wednesday in Ranong province and flagged down police for help, police Col. Kraithong Chanthongbai said. Twenty-one were hospitalized while the rest were detained for questioning, he said.
"When police got to the scene, they found that 54 of the workers were already dead in the packed container truck," Kraithong said.
Of the dead, 37 were women and 17 were men. Police did not immediately know what jobs they were heading for, but illegal Myanmar immigrants in that region generally work in the fishing and construction industries or as maids.
Police were searching for the truck's driver, who had fled the scene, and members of the smuggling gang they believed arranged the trip.
Kraithong blamed the driver for failing to turn on the air conditioning in the back of the truck, which normally was used to transport seafood.
The surviving workers told police they snuck into Ranong province from Myanmar's Victoria Point by fishing boat Wednesday night and were then packed into a small container truck for a trip to Phuket.
But after two hours, the workers told police that many of them began falling sick because of poor ventilation in the truck, Kraithong said.
The driver stopped the truck after being alerted to the problem but then fled the scene, Kraithong said.
Ranong province is about 460 kilometers (290 miles) south of Bangkok just across from Myanmar's Victoria Point, and is regarding as a major point of trade between the two countries.
There are about a million Myanmar workers registered to work in Thailand, and an additional million estimated to be in the country illegally to work mostly as laborers, joining hundreds of thousands from Cambodia and Laos.
The illegal workers lack legal protections and are often ruthlessly exploited.
Some of the Myanmar migrants flee their country to escape armed conflicts between ethnic minority rebels and the Myanmar army, and others for lack of economic opportunity in their impoverished country, one of the poorest in Asia.
The London-based human rights group Amnesty International found in a 2005 report that workers from Myanmar take jobs that Thais consider too dirty, dangerous or demeaning, "are routinely paid well below the Thai minimum wage, work long hours in unhealthy conditions and are at risk of arbitrary arrest and deportation."
Many also face great risk in reaching Thailand. In December, authorities recovered the bodies of 22 Myanmar migrants found floating off the west coast of Thailand in the Andaman Sea. They were believed to be trying to enter Thailand illegally.