Heavy monsoon rain heaped new misery on Sunday on hundreds of thousands of Muslim Rohingya stuck in makeshift camps in Bangladesh after fleeing violence in Myanmar, as authorities started a drive to force them to a new site.

With food and water shortages already making life tough, torrential rain brought back swamp-like conditions to many parts of the border town of Cox's Bazar which has become a magnet for the Rohingya.

About 7.7 centimetres of rain fell in 24 hours and more is predicted in the next two days, the Bangladesh Weather Department said.

Bangladesh authorities, who have already issued travel restrictions on the Rohingya, launched an operation late Saturday to get tens of thousands out of roadside camps and hillside shanties into a giant new camp.

The United Nations says 409,000 Rohingyas have now overwhelmed Cox's Bazar since August 25 when the military in Buddhist-majority Myanmar launched operations in Rakhine state.

As existing camps are already full with 300,000 Rohingya fleeing earlier violence, many of the Rohingya have been forced to live in the open air or under flimsy plastic sheets.

Police toured streets with loudspeakers ordering exhausted families to go to the Balukhali camp in Cox's Bazar, which is being cleared to build new shelters.

“We are shifting them from the roadsides where many of them have been staying,” Khaled Mahmud, a government spokesman for Cox's Bazar district told AFP.

Mahmud said gradually all the new Rohingya would be taken to Balukhali to bring order to the chaotic aid operation.

'Disaster unfolding'

On Saturday, Bangladesh police issued tough new orders banning the Rohingya from moving out of designated areas. The order even prevented them from taking shelter with friends and relatives.Checkpoints have been set up at key transit points.

With thousands more Rohingya arriving each day, Bangladesh authorities fear the refugees could swamp other towns and cities across the country.

But the United Nations is already warning of intolerable conditions in the camps around Cox's Bazar.The rain “has doubled their misery”, said Mohammed Kai-Kislu, police chief at Ukhia near Cox's Bazar, the new home for many Rohingya.

Aid workers said thousands of Rohingya were drenched by the return of the monsoon after a respite of a few days.

Arfa Begum and seven of her family tried to hide under rubber trees near the Balukhali settlement where they arrived five days earlier.

“They evicted us from the rubber plantation,” she said, referring to the police and border guards forcing the refugees out of makeshift shelters.

“It took hours to find a safe place. We were drenched,” she told AFP.

Faced with a spreading mudbath, the Rohingya have started building bamboo carpets to get over flooded land.

A human rights expert in Cox's Bazar urged the government to shut local schools for three days to allow the Rohingya to camp in them.

“It is another disaster unfolding. Thousands of Rohingya had no place to hide when the rain came,” Nur Khan Liton, who headed Bangladeshi rights group Ain O Salish Kendra, told AFP.

He said moving the Rohingya from roadsides and open spaces should be halted as it was compounding their troubles.

Suu Kyi to give speech

Conditions deteriorated for the Rohingya in what could be a key week in the crisis.

Myanmar's de-facto leader, Aung San Suu Kyi is to give a nationally televised speech on the Rohingya case on Tuesday.

The Nobel peace laureate, much criticised around the world for not condemning the violence against the Rohingya, must address the global outrage while not angering the military, which maintains huge power.

General Min Aung Hlaing, Myanmar's globe-trotting army chief, called for a “united” stance in handling the crisis but gave no sign of concessions.

Bangladesh Prime Minister Sheikh Hasina has arrived at the UN General Assembly in New York to press for greater help coping with the refugees and put more pressure on Myanmar over the case.

She is to address the UN assembly on Thursday.