"An estimated 370,000 Rohingya have entered Bangladesh after fleeing violence in Myanmar's Rakhine state since August 25," Joseph Tripura, a spokesman for the UN refugee agency, told AFP.
The true figure could be even higher as many new arrivals are still on the move and staying by the roadside, making it difficult to include them in the counting, the UN said.
It attributed the overnight jump from Monday's figure of 313,000 to the large numbers now moving off the roadside and into informal camps, where they can be counted more easily.
Attacks by Rohingya militants on Myanmar security forces in Rakhine on August 25 sparked harsh military reprisals and an exodus across the border to southeast Bangladesh.
The Muslim Rohingya minority community has long been subjected to discrimination in mostly Buddhist Myanmar, which denies them citizenship.
That has left tens of thousands of new arrivals with nowhere to shelter from the monsoon rains.
Most have walked for days and aid workers say many are sick, exhausted and in desperate need of shelter, food and water.
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