The grave site was found in Sadao district of Songkhla province at an abandoned camp for 'boatpeople' who had apparently been trafficked to Thailand's border area with Malaysia, a zone notorious for housing remote camps for trafficked migrants.
"There are 32 graves, four bodies have now been exhumed and are on their way... To hospital to for an autopsy," Sathit Thamsuwan a rescue worker, who was at the scene soon after the site was found, told AFP.
The local hospital confirmed the Bangladeshi man had survived and was in a stable condition.
The grisly discovery of the grave was also confirmed by a senior official from Sadao.
More From This Section
"There are more than 20 graves," he said, requesting anonymity.
"Military and border patrol police have now cordoned the area off so we can bring forensic officials to the site."
Tens of thousands of migrants from Myanmar -- mainly from the Rohingya Muslim minority -- and increasingly from Bangladesh make the dangerous sea crossing to southern Thailand, a well worn trafficking route often on the way south to Malaysia and beyond.
Thailand has been criticised in the past for pushing boatloads of Rohingya entering Thai waters back out to sea and for holding migrants in overcrowded facilities.
The ruling junta says it has taken significant steps to combat trafficking since June, when the United States dumped Thailand to the bottom of its list of countries accused of failing to tackle modern-day slavery.
In January, Thai authorities confirmed more than a dozen government officials -- including senior policemen and a navy officer -- are being prosecuted for involvement or complicity in human trafficking.