Myanmar and Bangladesh agreed to address the "root causes" of a migrant exodus from their shores at talks in Bangkok Friday, but critics pilloried a deal that failed to mention the Rohingya minority at the heart of the crisis.

Southeast Asia's migrant scandal began to unfurl at the start of this month after a Thai crackdown on people smuggling threw the multi-million dollar industry into disarray.

It led gangmasters to abandon their victims on land and at sea, and images of stick-thin, dazed migrants trapped on boats or stumbling onto shores and out of forests shocked the world, heaping pressure on Southeast Asian nations to act.

The majority of the migrants are Rohinyga Muslims, who are pariahs in Myanmar's Buddhist-majority western Rakhine State, and people fleeing poverty from neighbouring Bangladesh.

The Thai hosts described the day-long talks as "very constructive", saying all 17 countries at the meeting agreed on a statement to provide humanitarian help to 2,500 migrants believed to still be adrift at sea, as well as to the 3,500 who have already made it to Thai, Malaysian and Indonesian shores since May 1.

The statement also drew a commitment to address the "root causes" and "factors in areas of (migrants') origin", including improving the economy, human rights and security in the source countries.

But the document did not mention the Rohingya -- who Myanmar refuses to recognise as an official minority.

Myanmar denies citizenship to the majority of its 1.3 million Rohingya and calls them "Bengalis" -- shorthand for foreigners from neighbouring Bangladesh.

The publication on Friday of Myanmar's first census in three decades also failed to include the Rohingya in its tally, after authorities refused to count them if they identified themselves as part of that ethnic group.

In a timely development just as the Bangkok meeting wrapped up, Myanmar's Ministry of Information said it had rescued 727 "Bengalis" adrift in its waters on Friday morning.

Bangladesh recognises some 30,000 Rohingya as refugees but tens of thousands more are treated as illegal migrants from Myanmar.

Welcoming the outcome of the meeting, Shahidul Haque, head of the Bangladeshi delegation, told reporters "we had a very productive discussion today".