Unusually heavy monsoon rains have killed at least 283 people, destroyed crops, inundated hundreds of factories and damaged the homes or livelihoods of millions of people in Thailand, according to the government.
About 110,000 people around the country have sought refuge in shelters.
The National Flood Relief Centre warned water up to one metre (3.3 feet) deep was expected in Rangsit, Saimai, Lamlukka and Klongluang in Bangkok's northern suburbs, advising people living in one-storey buildings to evacuate.
But the authorities later reassured the public, saying they were close to repairing the broken dyke.
"There is really a lot of water but it is under our control," Bangkok governor Sukhumbhand Paribatra said on television. "It's not at a critical level. You can be worried but don't panic."
Inner Bangkok, including the main tourist districts, was not affected and conditions in most of the city remained normal.
Currently 26 out of 77 provinces are affected, while Bangkok is bracing for a large amount of run-off water to reach the city along with seasonal high tides that will make it harder for the flood waters to flow out to sea.
Central Bangkok is protected by flood walls and the authorities have piled sandbags along the Chao Phraya River to try to keep water out of nearby areas, whose residents are no strangers to seasonal floods.
"This year is the worst. It flooded around here every year but this year is the highest level," said Sukon Chadeth, a 36-year-old food seller living near the river.
The authorities are preparing to dredge and drain canals in the capital.
"We will dig deep and expand canals so the water can flow easily," said Prime Minister Yingluck Shinawatra. "I will assign military to take responsibility for it."
The floods have dealt a heavy blow to Thailand's economy. Japanese automakers such as Toyota have suspended production in the kingdom due to water damage to facilities or disruptions to parts supplies.
On Thursday, floodwater started pouring into Ayutthaya's Hi-Tech Industrial Estate -- home to about 140 plants which employ about 50,000 workers -- after a section of a dyke collapsed.
The ancient city of Ayutthaya, about 80 kilometres (50 miles) upriver of Bangkok, has been badly affected and the UN cultural organisation UNESCO said it would launch a mission to the World Heritage site to assess the impact.
Culture minister Sukumol Kunplome said it was unclear how much damage there was because the city was still under water.
"Once the water subsides, we can estimate our loss," she told AFP.
Flooding has also hit other countries in Southeast Asia, including Cambodia, where almost 250 people have died. In Vietnam, the death toll has risen to 43 and officials say most of the dead are children.
On the edges of Bangkok's Chao Phraya River, some residents were getting ready to leave their homes if necessary.
"Even though we have the barrier, we're not confident," said 34-year-old Boonluea Petchjun. "The water can come in any time so I already prepared by packing my important belongings and I am ready to evacuate any time."