|Hundreds have died and millions have been displaced during three months of heavy monsoon rains [AFP]
Thailand's prime minister has said that it was impossible to protect all of Bangkok from the country's worst floods in decades, describing the situation as a "national crisis".
Yingluck Shinawatra told reporters on Thursday: "We cannot block the water forever," adding that the government would choose which parts of the city to allow the water through to minimise the impact.
"The longer we block the water the higher it gets," she said. "We need areas that water can be drained through so the water can flow out to the sea."
The government has reinforced the city's floodwalls in an attempt to prevent the floods pouring into the densely populated city from the central plains, which are several metres under water in places.
Inner Bangkok has so far escaped major flooding as the authorities divert water to areas outside the main capital in a bid to prevent the Chao Phraya River bursting its banks and flooding the political and economic heartland.
But efforts to keep the city of 12 million people dry have been complicated by a seasonal high tide.
"Flood waters are coming from every direction and we cannot control them because it's a huge amount of water. We will try to warn people," Yingluck, who took power in August, said.
"This problem is very overwhelming. It's a national crisis so I hope to get co-operation from everybody."
Three months of heavy monsoon rains have killed 320 people, damaged the homes and livelihoods of millions of people, mostly in northern and central Thailand, and forced tens of thousands to seek refuge in shelters.
Currently, about one-third of Thailand's provinces are affected.
Flooding in areas directly north of the city worsened only days after some officials indicated the worst threat had passed.
Shinawatra’s government is now facing growing criticism over her government's conflicting messages and slow response to the floods.
Speaking to Al Jazeera, Sean Boonpracong, a government spokesman, said: "You have to understand that flood is about 38 per cent more than last year’s…There is a huge volume of water coming down [equal to] the size of Hurricane Katrina and our existing plans is incapable of handling such situations.
"For now, we are watching the situation closely. We are preparing to announce information should any situation arise."
Al Jazeera’s Wayne Hay, reporting from Bangkok, said: "The government is saying that parts of Bangkok will have to be sacrificed to protect the commercial heart of the city, and it seems that those areas that may be sacrificed are those suburbs to the north and to the east.
"They are already on alert. Evacuations have not been ordered yet, but the people have been ordered to be on standby and get their belongings to higher grounds."
The opposition Democrats are calling on the government to declare a state of emergency to make it easier to control people and stop them damaging dykes to ease the flooding in their own areas.
Sukhumbhand Paribatra , Bangkok’s governor, warned on Wednesday that seven districts in northern and eastern Bangkok were at risk of inundation because of a broken dyke.
He advised residents in those areas to unplug electrical appliances, move belongings to higher ground and study the city's evacuation plan, saying they had 24 hours to prepare for possible flooding.
The authorities have failed to protect a number of major industrial parks from the gushing brown water, which has inundated hundreds of factories, disrupting production of cars, electronics and other goods.
The government says more than half a million people have been left without work.
But most of Thailand main tourist attractions - including the southern islands of Samui, Phuket and Phi Phi - have been unaffected.
Bangkok's main airport is still operating as normal and its flood defences have been reinforced.
The damage from the floods is estimated at more than 100 billion baht [$3.3bn], according to the central bank on Thursday.