Some 15,000 Rohingya refugees are now under coronavirus quarantine in Bangladesh's vast camps, officials said Monday, as the number of confirmed infections rose to 29.
Health experts have long warned that the virus could race through the cramped settlements, housing almost a million Muslims who fled violence in Myanmar, and officials had restricted movement to the area in April.
Despite this, the first cases in the camps were detected in mid-May.
"None of the infections are critical. Most hardly show any symptoms. Still we have brought them in isolation centres and quarantined their families," Toha Bhuiyan, a senior health official in the surrounding Cox's Bazar area told AFP.
He said narrow roads to three districts of the camps -- where the majority of the infections were detected -- have been blocked off by authorities.
The 15,000 Rohingya inside these so-called blocks faced further restrictions on their movement, he said.
It comes as charity workers expressed fears over being infected in the camps as they worked without adequate protection.
Two of the areas under isolation are in Kutupalong camp, home to roughly 600,000 Rohingya.
"We are trying to scale up testing as fast as possible to make sure that we can trace out all the infected people and their contacts," Bhuiyan said.
Seven isolation centres with the capacity to treat more than 700 COVID-19 patients have been prepared, he said.
Officials hope to have just under 2,000 ready by the end of May, he added.
Mahbubur Rahman, the chief health official of Cox's Bazar, said authorities hoped this week they would double the number of tests being performed daily from 188.
He said further entry restrictions have been imposed on the camp, with a 14 day quarantine in place for anyone visiting from Dhaka.
"We are very worried because the Rohingya camps are very densely populated. We suspect community transmission (of the virus) has already begun," Rahman told AFP.
Bangladesh on Monday notched up a record single-day spike in coronavirus cases, with 1,975 new infections, taking the toll to 35,585 cases and 501 deaths.
In early April authorities imposed a complete lockdown on Cox's Bazar district -- home to 3.4 million people including the refugees -- after a number of infections.
But a charity worker with one of the many aid organisations active in the camps said Monday he and many others were "very worried".
"Fear and panic has gripped aid workers because many of us were forced to work without much protection," he told AFP without wishing to be named.
"Social distancing is almost impossible in the camps. There is very little awareness about COVID-19 disease among the refugees, despite efforts by aid agencies."
The lack of information is exacerbated by local authorities having cut off access to the internet in September to combat, they said, drug traffickers and other criminals.
More than 740,000 Rohingya fled a brutal 2017 military crackdown in Myanmar to Cox's Bazar, where around 200,000 refugees were already living.