The number of refugees arriving in Bangladesh from Myanmar since August 25 has risen to 480,000, international aid bodies say.
The refugees are fleeing a Myanmar military offensive launched in response to about 30 co-ordinated attacks by Rohingya Muslim insurgents on August 25.
"The change in the new arrivals figure ... is due, in large part, to the additional estimated 35,000 new arrivals settling in the two refugee camps, which was not reported in the last situation report," the Inter-Sector Co-ordination Group of aid agencies said in a statement.
Meanwhile Human Rights Watch says Myanmar is committing crimes against humanity, calling for the UN Security Council to impose sanctions.
The UN refugee agency called for a redoubling of international aid for the refugees - 60 per cent of them children.
A Myanmar government spokesman rejected the accusation of crimes against humanity, saying there was no evidence.
Myanmar has also rejected UN accusations that its forces are engaged in ethnic cleansing against Rohingya Muslims in response to co-ordinated attacks by Rohingya insurgents on the security forces on August 25.
Refugees arriving in Bangladesh have accused the army and Buddhist vigilantes of trying to drive Rohingya out of Buddhist-majority Myanmar.
"The Burmese military is brutally expelling the Rohingya from northern Rakhine state," said James Ross, legal and policy director at New York-based Human Rights Watch.
"The massacres of villagers and mass arson driving people from their homes are all crimes against humanity."