Burma's president Thein Sein headed to devastated rural regions where a state of emergency was declared after deadly monsoon rains displaced tens of thousands of people, flooded swathes of rice paddy and prompted fears of dams collapsing.

Thein Sein arrived yesterday at a military base in Sagaing Division, a major rice growing area where soldiers are coordinating a relief effort after a month of rain over all but two of Burma's 14 states.

Thein Sein had been coming under criticism, especially on social media, for not doing more to deal with the emergency. On Thursday, he urged Cabinet ministers to go out into the field to supervise flood relief operations, saying that since July 16, some areas of the country have become inundated by heavy rains that destroyed farmland, roads, rail lines, bridges and houses. Roads from central to northern Burma have been especially badly affected

The storms and floods have so far killed 21 people, with water levels as high as 2.5 metres in Sagaing and 4.5 metres in western Rakhine state, according to the government, which on Friday declared four regions disaster zones.

Burma was inundated throughout last month and storms since July 22 have "severely affected" between 67,000 and 110,000 people, according to the United Nations.

Though rain has stopped in most areas, the recovery effort is a major test for impoverished Burma. The country has only basic infrastructure and medical facilities and is ill-equipped to deal with disasters, as shown when Cyclone Nargis battered the Irrawaddy Delta in 2008, killing 130,000 people.

"It's an emergency situation we have never faced before," said Aung Zaw Oo, the local transport minister for Sagaing. "We have only two motor boats for the rescue process. The government plans to send more."

Nearly 525,000 acres of farmland has been affected, an area roughly the size of Luxembourg, and more than 34,000 acres of paddy fields damaged, mostly in the Sagaing, Kachin State, Bago and Rakhine state regions, the agriculture ministry said.

Television footage showed bridges damaged or shaking from the strong current of floodwater. Cattle were drowned or seen with only their noses poking above the flow of water.

Local TV quoted people in Sagaing, Shan state and Magway saying they were worried that dams already over their safe limit could collapse if more rain came.

There is particular concern about Rakhine state, where a tropical storm was moving from neighbouring Bangladesh. The situation in Rakhine is considered especially dangerous, because more than 100,000 internally displaced people who fled their homes due to civil conflict in recent years live in poorly built and badly situated camps

More than 150 tents were swept away by storm winds at a camp for Muslim Rohingyas in Rakhine, where the United Nations refugee agency was providing some help to a mostly stateless minority that already lives in harsh, apartheid-like conditions. The state's Mrauk Oo town was completely flooded.

"Even when food and relief goods were airlifted by helicopters to the flooded town, there was nowhere to store these goods and no roads for trucks to drive on," the state's Chief Minister Maung Maung Ohn told MRTV on Friday.