Local firefighter official Emdadul Haq said the 330 rough buildings, including homes and shops, in the Kutupalong Rohingya refugee camp were completely destroyed in the fire, which began at a gas cylinder shop.
"Ten people were injured in the accident. It's the biggest fire (to have broken out) in the camps" to date, he told AFP, adding another 300 shanties, most of them built with flimsy tarpaulin and bamboo, had been damaged by the fire.
No casualties have so far been reported in Kutupalong, one of the world's largest refugee camp, he added.
Bangladesh's deputy refugee commissioner Shamsud Douza said the injured were taken to local hospitals for treatment.
The UNHCR said it has mobilised an emergency response team to "help the affected refugees".
Read also: Rohingya refugees quarantined on Bangladesh island 'unfit for habitation'
More than a million Rohingya live in the squalid camps in Bangladesh's Cox's Bazar district, which includes Kutupalong.
Some 740,000 of them arrived in the South Asian nation in 2017 from Myanmar's conflict-ridden Rakhine state, escaping a brutal military clampdown.
Read also: Human Rights Watch urges Bangladesh to reverse 'inhumane' Rohingya boat push-backs
Experts and aid workers had already warned that fire could cause massive havoc in the overcrowded camp settlement.
"We have seen small fire accidents earlier but never saw such big devastation. Many people were trying to make a living by running small shops. They are affected the most," Rohingya community leader Abdur Rahim said.
In 2018, a fire in one of the camps killed a woman and three children.
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