The U.N. said Friday that an "alarming number" of 270,000 Rohingya Muslims have fled violence in Myanmar by crossing into Bangladesh in the last two weeks.

The new number confirmed Friday by U.N. Refugee Agency spokeswoman Vivian Tan is much higher than the 164,000 the agency had previously estimated had arrived since Aug. 25.

"This is an alarming number," Tan said. "The existing camps are full to the capacity. There is a lot of pressure on relief agencies to accommodate the rising numbers."

She said the new number were still a "rough estimate," and were based on an assessment that involved a host of aid agencies operating in the area.

Some aid groups also had identified "new pockets of people that we did not know about before, mainly in villages" where Bangladeshi communities had taken them in, but also some new settlements and clusters in difficult-to-access areas.

More spontaneous shelters were appearing, Tan said, and makeshift camps were expanding along roadsides.

She said it was possible some people who received help from multiple agencies could have been counted twice.

Associated Press reporters who have been in the area all week saw a surge in the number of Rohingya entering Bangladesh on Thursday and Friday.

An increasing number of Rohingya were also arriving by boat, with 300 boats reaching the Bangladesh town of Cox's Bazar from Myanmar on Wednesday alone, according to the International Organization for Migration.

"Sea routes are particularly dangerous this time of year, when boats are known to frequently capsize in rough seas," the IOM said in a statement.

The exodus from Myanmar's northern Rakhine state began Aug. 25 after Rohingya insurgents attacked police posts. The military responded with what it called "clearance operations" to root out any fighters it said might be hiding in villages of Rakhine state.

Journalists have seen village homes burning as recently as Thursday in the region of Buddhist-majority Myanmar.

It's not known how many Rohingya remain in Rakhine state. Previously the population had been thought to be roughly 1 million.

U.N. agencies have released $8 million in emergency aid, but were pleading for millions more in international aid to help the migrants.

There are now massive crowds of Rohingya in the streets of towns including Cox's Bazar and Teknaf, with relatively few soldiers or police and even fewer signs of aid agencies.

At a small makeshift mosque made of bamboo sticks and plastic sheets, a small group of new arrivals offered prayers Friday, the holiest day of the week in Islam.

Later, members of a local organization were seen distributing aid, throwing packets of puffed rice and old clothes into huge crowds of Rohingya. There are no clearly organized points of distribution.

Tan, of the refugee agency, said it was distributing aid through a local organization that preferred to keep a low profile.