An estimated 370,000 Rohingya Muslim refugees have fled to Bangladesh from violence in Myanmar since late August, a spokeswoman for the UN refugee agency, Vivian Tan says.
The government of Buddhist-majority Myanmar says its security forces are fighting Rohingya militants behind a surge of violence that began on August 25.
Many of the refugees say Myanmar authorities are intent on pushing Rohingya out of the country.
"The system is clearly at full stretch and needs all the support it can get," International Organisation for Migration chief spokesman Leonard Doyle said.
He declined to say how big he thought the exodus could get.
"Clearly the estimates have been bypassed several times over," he told a briefing in Geneva. "I'm reluctant to give a number but obviously people fear that it could go much higher."