NEW DELHI — A devastating fire that tore through a sprawling Rohingya refugee camp in Bangladesh killed 15 people and left tens of thousands homeless, the United Nations said Tuesday. More than 550 people were injured and 400 remain missing.

The fire began Monday afternoon at Balukhali camp, one of several such settlements in Cox’s Bazar in southern Bangladesh, which is home to nearly 1 million Rohingyas who fled from neighboring Myanmar.

Videos on social media showed thick, black smoke rising from the fire that ravaged the shanties in the densely populated camp.

“I was in my house when I saw the fire,” said Abdur Rahim, a refugee. “Many people who had their shelter burned down spent the night in the open.” One of his nephews is missing, he said.

A witness told the BBC she had never seen such a “devastating fire,” while another described how thousands of settlements had been “reduced to ashes.”

Louise Donovan, a spokeswoman for the U.N. High Commissioner for Refugees in Cox’s Bazar, said that at least 10,000 shelters were damaged and that nearly 45,000 people were displaced. The cause of the fire was not clear.

Government authorities and humanitarian workers pitched in with emergency supplies and drinking water.

Teams from the U.N. World Food Program provided meals and the Children’s Emergency Fund helped evacuate the refugees.

“Our priority is to secure the immediate safety, security and protection of children in coordination with the concerned authorities, first responders and partner organizations in the UN and NGO community,” Tomoo Hozumi, the UNICEF representative in Bangladesh, said in a statement.

Life is difficult in the crowded refugee settlements in Cox’s Bazar, with unsanitary conditions and higher rates of crime and trafficking. Last year, Bangladesh began an ambitious relocation drive to shift hundreds of Rohingyas to an island.

Human rights groups opposed the move, questioning the island’s habitability: Bhasan Char, which is 20 miles off the mainland, is at risk of flooding and submersion during the monsoon season.

Activists also have questioned whether those relocated had consented to the move. Brad Adams, Asia director of Human Rights Watch, said in December, “The Bangladesh government is actively reneging on its promise to the U.N. not to relocate any refugees to Bhasan Char island until humanitarian experts give a green light.”

Hundreds of thousands of Rohingya refugees fled to Bangladesh in 2017 after a military crackdown in Buddhist-majority Myanmar, where they are a persecuted minority group. U.N. experts have described the situation as “ethnic cleansing” and Myanmar has been accused of genocide under international law.

In January, more than 3,500 refugees were left homeless after a fire gutted a nearby camp.

Azad Majumdar contributed to this report from Dhaka, Bangladesh.