Thailand's catastrophic floods may take up to six weeks to recede as the the number of dead rose to 356 and more than 110,000 people are displaced, Prime Minister Yingluck Shinawatra said Saturday

Excessive monsoon rains have drowned a third of the country since late July, causing billions of dollars in damage and putting nearly 700,000 people temporarily out of work.

In a weekly radio address Saturday, Yingluck said that "during the next four to six weeks, the water will recede."

Colossal pools of runoff from the north have been bearing down on the capital for the last two weeks. In recent days, water has submerged districts just outside Bangkok's northern boundaries, while on Friday, floodwaters began spilling over canals within the city's outermost districts, causing damage to homes.

Thailand's prime minister has warned people of a potential deluge of floodwater over the weekend and is advising them to leave for higher ground. Sukree Sukplang/Reuters

Some flooding on Bangkok's outskirts was expected after Yingluck ordered floodgates opened in a risky move to drain the dangerous runoff through urban canals and into the sea. So far, most of the metropolis of nine million people has escaped unharmed, and its two airports are operating normally.

In the meantime, the government will step up aid to those whose lives have been disrupted, including 113,000 people Yingluck said were living in temporary shelters after being forced to abandon submerged homes.

The government said at least 356 people have died in the floods since July.

The floods are the worst to hit the country since 1942, and the crisis is proving a major test for Yingluck's nascent government, which took power in July after heated elections and is coming under fire for not acting quickly or decisively enough to prevent major towns north of the capital from being ravaged by floodwaters.

Electronics industry suffers

The Labour Ministry says the flooding has put nearly 700,000 people temporarily out of work, many of them from five major industrial estates north of Bangkok that were forced to suspend operations.

Among those affected are Japanese carmakers Toyota and Honda, which have halted major assembly operations. The electronics industry has also suffered, including computer hard drive make Western Digital, which has two major production facilities in the flooded zone.

In an interview published in the Bangkok Post, Science and Technology Minister Plodprasop Suraswadi said natural and manmade factors combined to create the crisis.

Seasonal monsoons came six weeks early and have lasted longer than usual, filling reservoirs, dams, and fields with 30 per cent more rainfall than average. At the same time, the government kept too much water in dams over the summer in a bid to save water for rice cultivation, Plodprasop said.

'We need co-operation and sacrifice from everyone.'—Prime Minister Yingluck Shinawatra

Overall, about 20 billion cubic metres of rainfall has drenched Thailand over the last several months, Plodprasop said. About half of that has already drained into the sea, leaving about 10 billion cubic metres of water threatening Bangkok, much of it spread across rice fields in Thailand's central plains.

Plodprasop said it will take about 20 more days to drain those floodwaters into the Gulf of Thailand, a task he said was complicated by the fact that the nation's irrigation system was designed to control water flows for farming and consumption — not to prevent floods.

"We have never faced such a huge mass of floodwater in the fields," Plodprasop said.

He said he believed inner Bangkok "should be safe, as we have an extensive drainage system with water pumps to drain excess water out quickly."

Thousands of cars are parked on elevated highways as drivers try to safeguard their vehicles.

"The flooding this time is a critical problem," Yingluck said. "We need co-operation and sacrifice from everyone."

To fight the crisis, Yingluck on Friday invoked her powers under a disaster law that gives her authority over all other official bodies, including local governments.

The move should allow better co-ordination with the municipal authorities in Bangkok and help project Yingluck as a take-charge leader, after weeks of seeming indecision and confusion.