Bangladeshi authorities are trying to restrict the movement of Muslim Rohingya refugees fleeing violence in Myanmar into crowded border camps and have started immunising tens of thousands of children against diseases.

Bangladesh has been overwhelmed with more than 400,000 Rohingya who fled their homes in the last three weeks amid a crisis the UN describes as ethnic cleansing.

Prime Minister Sheikh Hasina, wo has lambasted Myanmar for “atrocities,” left Dhaka to address the annual U.N. gathering in New York.

Hanida Begum’s wails filled the air as she mourned her dead boy. A Rohingya Muslim woman, who crossed over from Myanmar into Bangladesh, lies unconscious on the shore of Bay of Bangal after the boat she was traveling in capsized at Shah Porir Dwip, Bangladesh, Thursday, Sept. 14, 2017. Nearly three weeks into a mass exodus of Rohingya fleeing violence in Myanmar, thousands were still flooding across the border Thursday in search of help and safety in teeming refugee settlements in Bangladesh. (AP Photo/Dar Yasin) Hanida Begum’s infant son Abdul Masood died as the boat capsized in Shah Porir Dwip, Bangladesh. Fleeing the violence in Myanmar, the Rohingyas now have to find shelter. Naseer Ud Din holds his infant son Abdul Masood, as his wife Hanida Begum cries upon reaching the Bay of Bengal shore. Women wail as a relative lies unconscious after the boat capsize. A Rohingya Muslim woman, who crossed over from Myanmar into Bangladesh, shouts for help as a relative lies unconscious. A man shakes a Rohingya Muslim boy while trying to revive him after the boat he was traveling in capsized. Nearly three weeks into a mass exodus of Rohingya fleeing violence in Myanmar, thousands were still flooding across the border Thursday in search of help and safety in teeming refugee settlements in Bangladesh. Relatives carry a Rohingya Muslim woman, who fell unconscious when the boat she was traveling in capsized minutes before reaching shore, towards a medical center for treatment at Shah Porir Dwip.

Abdus Salam, a doctor in a state-run hospital in Cox’s Bazar district, says that some 150,000 children will be immunized over seven days for measles, rubella and polio. U.N. says there are some 240,000 children in dire conditions.

Police meanwhile are checking that the refugees don’t spread out to nearby towns.