A tropical cyclone headed toward Bangladesh and western Myanmar is raising fears of a potentially devastating humanitarian crisis in Myanmar's Rakhine state, where 140,000 Rohingya refugees displaced by sectarian violence are living in makeshift camps.

"Many of the camps are located in low-lying coastal areas, susceptible to tidal surge," said the United Nations Office for the Coordination of Humanitarian Affairs. The estimated 45,000 refugees living in Sittwe, Pauktaw, Myebon and Kyauktaw in Rakhine state are the...