BANGLADESH (REUTERS) - For a people under siege, these rickety boats may look like freedom.

They've ferried tens of thousands of Rohingya Muslims from Rakhine state to Bangladesh, to escape the deadly onslaught by Myanmar's army.

But safety comes at a cost, as much as US$120 (S$161.57) per adult to be exact.

Some refugees say they've been held to ransom by Bangladeshi fishermen if they can't pay for the trip, others have handed over family heirlooms, rings, gold necklaces. Anything to cover the exorbitant rates.

Bangladeshi officials say they're nothing more than human traffickers and have made arrests and even set fire to some boats.

The fishermen though tell a different tale, describing this as a moral call to help their Muslim brothers, and they say the little money they do take, pays for petrol.

More than 400,000 Rohingya have poured into Bangladesh in the last three weeks, fleeing what the UN calls a "textbook case of ethnic cleansing".

Thousands of others huddle on Myanmar's shores, waiting for their chance to make the five-hour journey, which is blurring the lines between rescuing and profiteering.