At least 20,000 Rohingya have fled a huge blaze engulfing shanty homes at refugee camps in southeastern Bangladesh, officials said Monday, in the third fire to hit the settlements in four days.

Nearly one million of the Muslim minority from Myanmar live in cramped and squalid conditions at the camps in the Cox's Bazar district, with many fleeing a military crackdown in their homeland in 2017. 

Officials said the fire was believed to have started in one of the 34 camps -- which span about 8,000 acres (3,237 hectares) of land -- before spreading to two other camps.

Thick columns of smoke could be seen billowing from blazing shanties in video shared on social media, as hundreds of firefighters and aid workers battled the flames and pulled the refugees to safety.

"It is a massive fire. At least 20,000 people fled their homes as the fire spread," Cox's Bazar administrator, Mamunur Rashid, told AFP.

"We doused the fire in one place and it spreads to other places."

Rashid said there were no reports so far of injuries or deaths.

Officials told AFP a preliminary assessment found that more than 900 shanties -- home to about 7,400 refugees -- had been gutted, with the blaze still burning.

Mohammad Yasin, a Rohingya helping with the firefighting, told AFP the blaze was still raging eight hours after it started and was the worst he had seen since 2017.

A Save the Children volunteer, Tayeba Begum, said "people were screaming and running here and there (and) children were also running scattered crying for their family".

It was the third blaze to hit the camps in four days, fire brigade official, Sikder, who only goes by one name, told AFP.

Two separate fires at the camps on Friday destroyed scores of shanties, officials said then.

Sikder said the cause of the fires were not yet known.

Two big blazes had also hit the camps in January, leaving thousands homeless and gutting four UNICEF schools.

Amnesty International's South Asia campaigner, Saad Hammadi, tweeted that the "frequency of fire in the camps is too coincidental, especially when outcomes of previous investigations into the incidents are not known and they keep repeating".

The government has meanwhile been pushing the refugees to relocate to a remote island in the Bay of Bengal, saying the camps were too crowded.

So far, 13,000 Rohingya have been moved to the flood-prone island that critics say is in the path of deadly cyclones.