Authorities in Bangladesh have begun a survey to determine the exact number of Rohingya Muslims who have fled persecution in majority-Buddhist Myanmar.

The director of the survey says Bangladesh's Bureau of Statistics began the exercise this week with the help of the International Organization of Migration.

Alamgir Hossain said the survey across six districts will end on Wednesday and will be followed by a census of Rohingya next month.

Around 33,000 Rohingya have been documented in two official camps in the southern coastal district of Cox's Bazar that borders Myanmar.

Bangladeshi officials say another 300,000 to 500,000 Rohingya remain unaccounted.