The Rohingyas - a distinct Muslim ethnic group who are effectively stateless - have been fleeing Myanmar for decades. But a combination of factors means many are now stranded in rickety boats off the coasts of Thailand, Malaysia and Indonesia with dwindling supplies of food and water.
Also on the boats are thousands of economic migrants from Bangladesh fleeing grinding poverty at home.
Why are the Rohingyas fleeing Myanmar?
While the Rohingyas say they are descendants of Arab traders who have been in the region for generations, Myanmar's governments say they are not a genuine ethnic group but are actually Bengali migrants. Successive Myanmar governments have been introducing policies to repress the Rohingya since the 1970s, according to Burmese Rohingya Organisation UK (Brouk).
migration route of Rohingya and Bangladeshis
They are denied basic services and their movements are severely restricted. The repression of the Rohingyas has gradually intensified since the process of reforms introduced by President Thein Sein in 2011, Brouk says. In June and October 2012 there were large scale attacks on Rohingyas in Rakhine State following the gang rape of a Buddhist woman.
In addition, the government in March revoked temporary registration certificates issued to hundreds of thousands of Rohingyas, meaning they can no longer vote.
So inflammatory is the Rohingya issue that opposition leader Aung San Suu Kyi has been criticised for failing to raise it.
In the past three years, more than 120,000 Rohingyas have boarded ships to flee abroad, according to the UN refugee agency. It says 25,000 migrants left Myanmar and Bangladesh in the first quarter of this year, about double the number over the same period last year. Between 40-60% of the 25,000 are thought to originate from Myanmar's western state of Rakhine.