Muslims fleeing oppression in Myanmar to Bangladesh rose to about 250,000, a quarter of the total Rohingya population, according to new figures provided by the United Nations.
News agencies quoted testimonies of shocking killings, rape and arson suffered by the refugees who managed to flee across the river that separates the two countries.
In the last two weeks alone 164,000 mostly Rohingya civilians have fled to Bangladesh, overwhelming refugee camps that were already bursting at the seams.
Scores more have died trying to flee the fighting in Myanmar's Rakhine state, where witnesses say entire villages have been burned since Rohingya militants launched a series of coordinated attacks on Aug 25, prompting a military-led crackdown.
Human Rights Watch obtained satellite data and images that are consistent with widespread burnings in northern Rakhine State, encompassing the townships of Rathedaung, Buthidaung, and Maungdaw. To date, Human Rights Watch has found 21 unique locations where heat sensing technology on satellites identified significant, large fires.
Police in Bangladesh say they have recovered the bodies of 17 people, many of them children, who drowned when boats packed with Rohingya refugees sank at the mouth of the Naf river.
Bangladesh border guards say desperate Rohingya are attempting to cross using small fishing boats that are dangerously overcrowded.
At least five capsized, leaving more than 60 people dead, police and border guards say.
Rohingya refugee Tayeba Khatun said she and her family had waited four days for a place on a boat after fleeing her township in Rakhine.
"People were squeezing into whatever space they could find on the rickety boats. I saw two of those boats sink," she told AFP inside Bangladesh. "Most managed to swim ashore but the children were missing."
Those flocking into Bangladesh have brought with them harrowing testimony of murder, rape and widespread arson by Myanmar's army.
Most have walked for days and the UN says many are sick, exhausted and in desperate need of shelter, food and water.
The camps which hosted around 400,000 refugees before the latest influx are now completely overwhelmed, leaving tens of thousands of new arrivals with nowhere to shelter from the monsoon rains.