Floodwaters lapped Bangkok's largest outdoor market Saturday as officials warned that there were no major barriers between the water and the heart of the Thai capital, less than 6 miles  away.

The country's worst flooding in half a century has affected more than a third of the country's provinces and killed almost 450 people nationwide. It has been spreading across Bangkok's north and west for more than a week, and officials have been struggling to protect the economically vital center of the city of 9 million people.

Hoping to divert some of the mass of water still piled up in northern Bangkok, workers Friday night completed a 3.7-mile flood wall made from massive, hastily assembled sandbags, said Bangkok city spokesman Jate Sopitpongstorn. But the city will have to rely on its existing drainage system to fight water that was already beyond the wall and just a few miles from the central business district, he said.

Over the past two decades, the city's much enlarged and improved drainage system has been able to effectively siphon off water during monsoon seasons with average rainfall. But it will be put to a severe test given the volume of water not seen in Bangkok since perhaps a great flood in the 1940s.

Sound predictions are difficult because various government officials, including the Bangkok governor and prime minister, have given often widely different versions of what can city residents can expect.

Water flowed past the eastern side of the famed Chatuchak Weekend Market, a sprawling, open-air shopping zone and major tourist attraction north of the central business district. Associated Press reporters saw only a few vendors and shoppers on a day that would normally be packed with sellers and buyers.

The floodwaters were also advancing southward in adjacent Lad Phrao, a district studded with office towers, condominiums and a popular shopping mall.

The floods, fed by unusually heavy monsoon rains and a string of tropical storms, started in northern Thailand in late July. They have destroyed millions of acres of crops and forced thousands of factories to close, though few of the country's most popular tourist areas have been affected.

The government has asked residents in eight of the city's 50 districts to evacuate and said Saturday that Bangkok authorities have set up 231 evacuation centers capable of holding more than 65,000 people. More than 10,000 people have flocked to 121 of these shelters so far.

Prime Minister Yingluck Shinawatra told a radio audience Saturday that a plan to be put before the Cabinet on Tuesday would allocate 100 billion baht ($3.3 billion) for post-flood reconstruction.

"I admit that this task has really exhausted me, but I will never give up. I just need the public to understand," Yingluck said.

Jate, the city spokesman, denied a newspaper report that authorities would not defend Bangkok's key link to its southern provinces. He said the city will seek to divert any water headed into the area via a canal to the Thachin River west of the city.

While some roads out of the capital are still passable in every direction, the two major safe corridors from the city run to the south and the east, where Bangkok's international airport is located. Officials maintain they are confident that Suvarnabhumi Airport -- the city's only aerial gateway to the outside world-- will remain open. Bangkok's second airport, used for domestic flights, is already underwater and remains closed.