The impending cyclone and monsoon season mean the Rohingya refugees now face more life-threatening dangers from the weather and environmental conditions in Bangladesh.
UN migration agency on Monday said most of these people, after escaping violence in their homeland, now live in extremely basic shelters in desperately overcrowded camps built on steep and precarious sandy slopes at severe risk of deadly landslides and flooding.
With UK support, IOM is helping to provide lifesaving shelter, medical care, protection and other vital services to refugees and host communities in the Cox's Bazar area.
The UN agency's emergency preparations are already being put into action and the organisation is now working with the government of Bangladesh as well as members of the local and refugee communities to help mitigate against major disasters in the weeks ahead, said the IOM.
Time is, however, running out and the size of the camps and scale of the environmental challenges where they are situated means agencies and the government must be ready to response to major emergencies, said the UN agency.
UNB said British Foreign Secretary Boris Johnson recently met with Rohingya refugees in Bangladesh and described as "unimaginable" the conditions they will face when the monsoon hits their camps in coming weeks.
Mr Johnson, who also met with state counsellor Aung San Suu Kyi in Myanmar on Sunday promised to help after refugees broke down in tears while telling him their experiences, fears and concerns at a meeting hosted by IOM.
Over 688,000 Rohingya have sought safety in the Cox's Bazar area of Bangladesh since late August 2017 after fleeing violence in Myanmar, with more continuing to arrive every week.
Johnson described suffering of the Rohingya as "one of the most shocking humanitarian disasters of our time".