The Thai government said Sunday it would set up a distribution centre in Bangkok to help replenish empty supermarket shelves as residents readied for floods that have so far largely spared the capital.

Deputy Prime Minister Kittirat Na-Ranong said making essential supplies available in one central place would allow stores whose supply chains have been interrupted to quickly stock up "as many items are missing from the shelves."

Supermarkets in the city have been busy with people loading up on food and bottled water as the low-lying capital remained on alert to be hit by the deadly floods that have plagued other parts of the country for weeks.

"Companies that produce consumer products have not been much affected (by the floods), so we will try to deliver products to a wider area," said Kittirat, who is also Thailand's commerce minister.

The government also said it would discuss in a cabinet meeting on Tuesday measures to help the nation's hundreds of flood-affected factories get back on track, with financial aid and tax incentives among the ideas mooted.

Three months of heavy monsoon rains have killed more than 350 people in Thailand and damaged the homes and livelihoods of nine million people.

More than 110,000 evacuees have been forced to seek refuge in 1,743 shelters from waters that the government has described as unstoppable.

In the capital, the authorities are battling the slowly advancing floods on several fronts, with parts of the northern outskirts of Bangkok already under waist-deep water.

The city centre remained dry as a sunny weekend drew to a close.

Residents however stayed on the alert after Prime Minister Yingluck Shinawatra told the city to prepare for possible inundation up to one metre (three feet) deep.

She also warned it could take six weeks for the flooding to recede.

The government is desperately trying to drain billions of cubic metres of water from upcountry out to sea through rivers and canals in and around the city by opening sluice gates in the capital -- a risky strategy.

"There are several factors that we can't control. The water is coming in two directions," Yingluck told reporters.

"Bangkok residents will be affected because water will flow down, particularly through the Saen Saeb canal (which crosses the city centre) and the drainage system which will help water to be diverted out quickly."

Another major test is expected between October 28 and 30 when seasonal high tides flow up the Chao Phraya, meeting run-off water from the north.

Thai troops on Sunday reinforced vulnerable barriers along Bangkok's Chao Phraya river after a sudden rise in the water level but no new flooding was reported.

The swollen river briefly overflowed Saturday in parts of five central Bangkok districts -- including near the political heartland -- prompting a race to fix the leaks.

The Bangkok authorities have urged about 3,000 people living on the banks of the Chao Phraya on the river side of the flood barriers to move to emergency shelters.

In the north of the city, meanwhile, the floods were closing in Bangkok's second-largest airport, Don Mueang, part of which has been turned into a refuge for thousands of evacuees and is defended by walls of sandbags.

The planned food distribution centre would also be located at the Don Mueang airport compound, the government said.

Most of Thailand's top tourist destinations and the capital's main airport have so far been unaffected.

Tens of thousands of soldiers and police have been mobilised to maintain order.

The government's flood relief centre said that floodwater in Pathum Thani province, just north of Bangkok, had been found to contain toxic chemicals and pollution experts were investigating the cause.

Conditions are desperate for flood victims who stayed behind, some using homemade floating devices in waters up to their necks.

"I've never seen anything like this in my life," Boonchu Thongtha told AFP in Rangsit, Pathum Thani where the water is chest deep.

"I can't go to the toilet, I can't do anything. My biggest fear is to not have food to eat. Our stored food is finished. I don't know what to do. We have nine people in the family," the 62-year-old told AFP.