More than half a million Rohingya refugees have flooded into Bangladesh to flee an offensive by Myanmar's military that the United Nations has called 'a textbook example of ethnic cleansing'.

The refugee population is expected to swell further, with thousands more Rohingya Muslims said to be making the perilous journey on foot toward the border, or paying smugglers to take them across by water in wooden boats.

Hundreds are known to have died trying to escape, and survivors arrive with horrifying accounts of villages burned, women raped, and scores killed in the 'clearance operations' by Myanmar's army and Buddhist mobs that were sparked by militant attacks on security posts in Rakhine state on August 25, 2017.

Myanmar's de facto leader Aung San Suu Kyi is 'appalled' at the Rohingya refugee crisis in her country and is determined to fix it, but needs to be careful not to inflame the situation further, an adviser to Suu Kyi told reporters on Friday.

'She is appalled by what she has seen. She does care deeply about this. I know that does not always come across. But she really does,' said the adviser, who asked not to be quoted by name.

Aid agencies now estimate that 536,000 people have now arrived in Cox's Bazar district, straining scarce resources of aid groups and local communities.

What the Rohingya refugees flee to is a different kind of suffering in sprawling makeshift camps rife with fears of malnutrition, cholera, and other diseases.