Dozens of visibly weak-looking people were on the deck of the stricken vessel, which was found apparently adrift several kilometres off the southern Thai island of Koh Lipe, in the Andaman Sea.
"About 10 people died during the journey. We threw their bodies into the water," one migrant shouted in Rohingya to a boat carrying reporters.
"There are 300 of us.... we have been at sea for two months. We want to go to Malaysia but we have not reached there yet."
A group of scarf-wearing woman huddled on the deck cried as reporters approached, the AFP reporter said, adding many of the passengers were young children, some seemingly toddlers.
The words "We are Myanmar Rohingya" were daubed in English on a black flag tethered to the boat, while a large tarpaulin had been erected to protect the stricken and weak migrants from the sun.
There was no immediate sign of Thai authorities who have apparently been scouring the area for a number of vessels laden with migrants adrift in the area.