The death toll from massive flooding in Myanmar in the wake of Typhoon Yagi has doubled to 226, state media reported, as the UN warned as many as 630,000 people could need help.

Yagi swept across northern Vietnam, Laos, Thailand and Myanmar more than a week ago with powerful winds and an enormous amount of rain, triggering floods and landslides that have killed more than 500 people, according to official figures.

State TV in junta-ruled Myanmar confirmed 226 fatalities late on Monday, with 77 people missing, doubling the previous toll of 113. The broadcaster also said nearly 260,000 hectares of rice paddies and other crops had been destroyed by floods.

The United Nations Office for the Coordination of Humanitarian Affairs disaster response agency said an estimated 631,000 people had been affected by flooding across Myanmar.

Food, drinking water, shelter and clothes are all urgently needed, UNOCHA said, warning blocked roads and damaged bridges were all severely hampering relief efforts.

Poor communication, particularly with remote areas, has also meant information about casualties has been slow to come out.

More than 150,000 homes were flooded, state newspaper the Global New Light of Myanmar reported, and the junta has opened more than 400 relief camps.

The UN's World Food Programme on Monday said the floods were the worst in Myanmar's recent history, without giving precise details.

Severe flooding hit the country in 2011 and 2015, with more than 100 deaths reported on both occasions, while in 2008 Cyclone Nargis left more than 138,000 people dead or missing. The junta issued a rare appeal for foreign aid at the weekend, with neighbor India so far the only country to respond, sending 10 tonnes of materials, including dry rations, clothing and medicine.

UNOCHA said more resources are urgently needed.

In recent years Myanmar's military has blocked or frustrated humanitarian assistance from abroad, including after powerful Cyclone Mocha last year when it suspended travel authorisations for aid groups trying to reach around a million people.

Even before the latest floods, people in Myanmar were grappling with the effects of three years of war between the junta and armed groups opposed to its rule, with millions forced from their homes by the conflict.

Across southeast Asia, hundreds of thousands of people have been forced to flee over the past week as Yagi rains swelled rivers and creeks beyond bursting point.

Many had to wade through murky brown waters up their chins, while others used whatever means they could -- including elephants in Myanmar and jetskis in Thailand.

Thailand's northern provinces were hit hard, with one district reporting its worst inundations in 80 years.

The death toll in the kingdom rose to 15 on Tuesday, according to new figures from the Department of Disaster Prevention and Mitigation.

Prime Minister Paetongtarn Shinawatra's government has announced financial aid of up to $6,000 per household for those affected by the floods.

In Vietnam, the death toll stands at 292, with 38 missing, more than 230,000 homes damaged and 280,000 hectares of crops destroyed, according to authorities.

Yagi, the strongest typhoon to hit the north of the country in decades, tore across the densely populated Red River delta -- a vital agricultural region that is also home to major manufacturing hubs -- damaging factories and infrastructure, and inundating farmland.

The typhoon caused an estimated 40 trillion dong ($1.6 billion) in economic losses, state media reported, citing an initial government assessment. (AFP)