A drone attack on Rohingya fleeing Myanmar killed many dozens of people, including families with children, several witnesses said, describing survivors wandering between piles of bodies to identify dead and injured relatives.

Four witnesses, activists and a diplomat described drone attacks on Monday that struck down families waiting to cross the border into neighbouring Bangladesh.

A heavily pregnant woman and her 2-year-old daughter were among the victims in the attack, the single deadliest known assault on civilians in Rakhine state during recent weeks of fighting between junta troops and rebels.

Three of the witnesses told Reuters on Friday that the Arakan Army was responsible, allegations the group denied. The militia and Myanmar's military blamed each another. Reuters could not verify how many people had died in the attack or independently determine responsibility.

Videos posted to social media showed piles of bodies strewn across muddy ground, their suitcases and backpacks scattered around them. Three survivors said more than 200 had died while a witness to the aftermath said he had seen at least 70 bodies.

Reuters verified the location of the videos as just outside the coastal Myanmar town of Maungdaw. Reuters was not able to independently confirm the date the videos were filmed.

One witness, 35-year-old Mohammed Eleyas, said his pregnant wife and 2-year-old daughter were wounded in the attack and later died. He was standing with them on the shoreline when drones began attacking the crowds, Eleyas told Reuters from a refugee camp in Bangladesh.

"I heard the deafening sound of shelling multiple times,” he said. Eleyas said he lay on the ground to protect himself and when he got up, he saw his wife and daughter critically injured and many of his other relatives dead.

A second witness, Shamsuddin, 28, said he survived with his wife and newborn son. Also speaking from a refugee camp in Bangladesh, he said that after the attack many lay dead and ”some people were shouting out from the pain of their injuries”.

Boats carrying fleeing Rohingya, members of a mostly Muslim minority who face extreme persecution in Myanmar, also sank in the Naf River that separates the two countries on Monday, killing dozens more, according to two witnesses and Bangladesh media.

Medecins Sans Frontieres said in a statement the aid organisation had treated 39 people who had crossed from Myanmar into Bangladesh since Saturday for violence-related injuries, including mortar shell injuries and gunshot wounds. Patients described seeing people bombed while trying to find boats to cross the river, the statement said.

A spokesperson for the United Nations High Commission for Refugees said the agency was “aware of the deaths of refugees from the capsize of two boats in the Bay of Bengal” and it had heard reports of civilian deaths in Maungdaw but that it could not confirm the numbers or circumstances.