Rescue workers in Myanmar are racing to help tens of thousands of people facing severe floods, as the death toll climbed to at least 46, officials have said.

Phyu Le Le Tun, Myanmar's relief and resettlement director, told Al Jazeera that at least 217,000 people have been affected in the country, after monsoon rains triggered flash floods and landslides, destroying thousands of houses, farmland, bridges and roads.

She also said that four people remain missing since the floods began.

Authorities have declared the four worst-hit areas in central and western Myanmar "national disaster-affected regions".

In the northern Sagaing region, residents said the flood waters caught them off guard as they swept into villages, engulfing homes and fields.

'No warning'

"There was no warning ... we thought it was normal [seasonal flooding]," Aye Myat Su, 30, told the AFP news agency from a monastery being used as a temporary shelter in the regional capital of Kalay.

"But within a few hours, the whole house was under water. My husband had to get onto the roof as there was no way out."

Landslides in Chin State - south of Sagaing - have destroyed 700 homes in the state capital Haka, while more than 5,000 people in another district are in relief camps, the state-backed Global New Light of Myanmar reported on Monday.

In Pictures: Myanmar inundated by floods

President Thein Sein has promised the government will do its "utmost" to provide relief, but said parts of Chin had been "cut off from surrounding areas", the report added.

Myanmar's health ministry says it is distributing medical supplies across the country including chlorine tablets, although it was unclear how many of the afflicted zones could be reached, with boats and helicopters in short supply.

Rains have also battered Rakhine State, which hosts about 140,000 displaced people, mainly Rohingya Muslims, who live in exposed makeshift coastal camps following deadly 2012 unrest between the minority group and Buddhists.

Regional flooding

Hundreds have also perished in recent days in India, Nepal, Pakistan and Vietnam following floods and landslides caused by heavy seasonal rains.

The flooding has claimed the lives of at least 100 people in India, officials there said on Sunday.

Another 109 have died in Pakistan over the past two weeks, according to authorities there.

Meanwhile in Vietnam rescuers were battling toxic mudslides from flood-hit coal mines in the northern province of Quang Ninh, home to the UNESCO-listed Ha Long Bay tourist site.

Seventeen people have been killed in recent flooding in Vietnam, including two families who were swallowed up by the toxic mud.