The number of Rohingya, a predominantly Muslim ethnic group, who have fled from Myanmar to Bangladesh since border clashes erupted five days ago has reached at least 18,500, the United Nations’ International Office of Migration said on Wednesday.

Thousands more are unable to cross the border, according to the migration office, or have found temporary shelter in Sittwe, the capital of the restive state of Rakhine in western Myanmar.

Most of those making the journey are women, children and elderly people.