Bangladesh coast guards have found the bodies of 20 people who drowned fleeing Myanmar, amid a rising exodus from Rakhine state.
The group, mostly women and children from the Rohingya minority, were trying to escape a recent surge of violence.
The crisis erupted after Rohingya rebels attacked 30 police stations last Friday, triggering a military response.
More than 100 people, mostly insurgents, have been killed and more than 27,000 Rohingya Muslims have fled.
Authorities in Bangladesh have warned that people are becoming increasingly desperate and attempting to escape by boat.
A coast guard official told AFP news agency the migrants were trying to flee on “rickety inland fishing boats” poorly equipped for the rough seas around Bangladesh.
The authorities in Bangladesh – which already hosts hundreds of thousands of refugees from Myanmar – have been sending many back.
The UN in Bangladesh said on Thursday that some 27,400 were estimated to have crossed the border since Friday, up from 18,000 a day earlier.
Thousands more people are thought to be trapped in an unoccupied zone between the countries.
Aid workers giving emergency shelter and food in Bangladesh said the refugees were in a “very desperate condition”.
“People are traumatised,” said Sanjukta Sahany of the International Organization for Migration (IOM). Some of the new arrivals had recent bullet wounds, aid workers said.
Rakhine, the poorest region in Myanmar (also called Burma), is home to more than a million Rohingya.
The Rohingya have faced decades of persecution in Buddhist-majority Myanmar, where they are not considered citizens. There have been waves of deadly violence in recent years.
The current upsurge is the most significant since October 2016, when nine policemen died in attacks on border posts.
The violence comes just days after an international commission led by former UN chief Kofi Annan warned of more radicalisation if ethnic tensions were not addressed. (Courtesy BBC)