The number of Rohingya Muslims to have crossed into Bangladesh from Burma has surged, according to the UN, with an estimated 270,000 arriving in the past two weeks.

The new number, confirmed by UNHCR spokeswoman Vivian Tan, marks a major increase from the 164,000 estimated on Thursday to have arrived since August 25.

The exodus began after Rohingya insurgents attacked police posts in Burma, prompting the military to respond with "clearance operations" to root out any fighters hiding in villages in Rakhine state.

Journalists have reported seeing village homes burning as recently as Thursday in the region of Buddhist-majority Burma.

Ms Tan said the number rose quickly in a single day mainly because aid agencies had spotted new settlements in the area. She said many areas where the refugees are located are difficult to access.

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

Her agency said Rohingya "are now squatting in makeshift shelters that have mushroomed along the road and on available land".

International agencies have released 8 million US dollars (£6 million) in emergency aid to help the migrants.

The International Organisation for Migration said an increasing number of Rohingya were arriving by boat, with 300 vessels reaching the Bangladesh town of Cox's Bazar from Burma on Wednesday alone.

"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.

It is not known how many Rohingya remain in Rakhine state. Previously the population had been thought to be about a million.