A top U.N. official said Saturday Bangladesh's plan to build the world's biggest refugee camp for 800,000-plus Rohingya Muslims was dangerous because overcrowding could heighten the risks of deadly diseases spreading quickly.

The arrival of more than half a million Rohingya refugees who have fled an army crackdown in Myanmar's troubled Rakhine state since August 25 has put an immense strain on already packed camps in Bangladesh.

Hard-pressed Bangladesh authorities plan to expand a refugee camp at Kutupalong near the border town of Cox's Bazar to accommodate the Rohingya. But Robert Watkins, the U.N. resident coordinator in Dhaka, told AFP the country should instead look for new sites to build more camps.

"When you concentrate too many people into a very small area, particularly the people who are very vulnerable to diseases, it is dangerous," Watkins told AFP. "There are stronger possibilities, if there are any infectious diseases that spread, that will spread very quickly," he said, also highlighting fire risks in the camps.

"It is much easier to manage people, manage the health situation and security situation if there are a number of different camps rather than one concentrated camp."

An estimated 331,000 Rohingya have already set up makeshift shelters in the area before construction begins, according to Watkins. Bangladeshi officials said the new camp will help them better handle relief operations and manage security amid fears that dispersed camps could become recruiting grounds for militants.