The United Nations launched one of its biggest ever cholera vaccination drives in the vast refugee camps of southeast Bangladesh Tuesday amid fears of an outbreak among nearly a million Rohingya now living there.

Thousands of Rohingya men and women lined up in intense heat at makeshift health centres on Tuesday, many with young children in their arms, to receive the oral vaccine against the disease.

The UN is working with the Bangladesh government to vaccinate 650,000 people living in the sprawling camps against cholera, which spreads through dirty water and can kill if left untreated.

"These people lack most of the basic services -- toilets, water sanitation and everything," UNICEF spokesman A M Sakil Faizullah told AFP.

"When we have this kind of situation, there's a heavy possibility of a cholera outbreak."

Nearly 520,000 Rohingya Muslims have arrived in Bangladesh since late August, fleeing a military crackdown in neighbouring Myanmar that the UN has said likely amounts of ethnic cleansing.

Poor and overpopulated Bangladesh has struggled to cope with the mass influx of people, many of whom have to travel for days or even weeks to reach safety and arrive exhausted and malnourished.

The influx had slowed in recent weeks, but now appears to have picked up again. An estimated 10,000 new refugees arrived on Monday.

World Health Organization workers supported by around a thousand local volunteers plan to vaccinate 650,000 Rohingya over the coming weeks.

They will follow up with a second dose of the vaccine for an estimated 250,000 children aged between one and five. Those under one will not be vaccinated.

It is thought to be the second biggest such campaign ever, after 800,000 people were immunised against the disease in Haiti in November.

Volunteers at the Thankhali camp used loudhailers to appeal to refugees to go to the centres, where they queued to have the vial placed in their mouths.

"The health workers told us we would be better with medicines, that we wouldn't have any more diseases," said Nabi Hossain, a 35-year-old refugee who arrived at the camp two weeks ago, as he queued with two of his sons.

Abdus Salam, a senior health official with the local government, said workers would go door to door to ensure no refugees were left out of the drive.

The Rohingya are a stateless Muslim minority who have long faced persecution in Myanmar, which regards them as illegal immigrants from Bangladesh.

The UN says more than 600,000 have arrived in the last year, swelling camps that were already home to between 300,000 and 400,000 refugees.

Bangladesh has allocated land to accommodate some 800,000 refugees in one massive camp, but the UN has warned that such a large concentration in one area could promote the spread of disease.