COX'S BAZAR (REUTERS) - Humanitarian organisations helping Rohingya Muslim refugees in Bangladesh said on Wednesday (Oct 4) they need US$434 million (S$590 million) over the next six months to help up to 1.2 million people, many of them children, who need life-saving help.

There are an estimated 809,000 Rohingya sheltering in Bangladesh after fleeing violence and persecution in Myanmar, more than half a million of whom have arrived since Aug 25 to join 300,000 Rohingya who were already in Bangladesh.

"The Rohingya population in Cox's Bazar is highly vulnerable, many having experienced severe trauma, and are now living in extremely difficult conditions," Robert Watkins, United Nations resident coordinator in Bangladesh, said in a release, referring to the Bangladeshi border district where most of the Rohingya are living.

Bangladesh and humanitarian organisations are struggling to help the 509,00 Rohingya who have arrived since Aug 25, when attacks by Rohingya militants triggered a Myanmar military offensive that the UN has branded ethnic cleansing.

Myanmar rejects accusations of ethnic cleansing. It says its security forces are fighting insurgents of the Arakan Rohingya Salvation Army who claimed responsibility for attacks on about 30 police posts and an army camp on Aug 25.

The insurgents were also behind similar but smaller attacks in October last year that also led to a brutal Myanmar army response triggering the flight of 87,000 Rohingya to Bangladesh.

The agencies' plan factors in the possibility of another 91,000 refugees coming, as the influx was continuing day to day, Mr Watkins said.

"The plan targets 1.2 million people, including all Rohingya refugees, and 300,000 Bangladeshi host communities over the next six months," he said.

"A rapid response from donors to this response plan is essential if the humanitarian organisations are to move ahead with critical activities to save lives, and provide protection to Rohingya refugees in Bangladesh," Mr Watkins said.