Myanmar's navy briefly detained and turned back journalists on Sunday near a migrant boat being held off the country's southern coast, according to Reuters witnesses, as officials remained guarded over what would be done with the people on board.

Before being turned away, Reuters reporters saw hundreds of migrants — some rake thin — crammed on the deck of the converted Thai fishing boat that had been intercepted in the Andaman Sea on Friday and held in the waters off Leik island.

Some were sat on two of the four Myanmar navy vessels standing off the fishing boat, which had been discovered carrying 727 migrants.