Bangkok flood
© Paula Bronstein/Getty ImagesThai women use plastic containers in an attempt to bale floodwaters out of their home in Bangkok on Thursday.
Waters flood northern suburbs, swamp Don Muang airport and close in on city centre

By boat, truck and bamboo raft, residents evacuated Bangkok's outer suburbs on Thursday as rising floods - which have claimed close to 400 lives across Thailand since July - closed in on the centre of the capital.

Prime Minister Yingluck Shinawatra, apparently close to tears as she briefed the media on Thailand's worst flooding for half a century, warned Bangkok's 12 million residents "we're fighting against the forces of nature" and said flood waters were damaging several of the city's dykes. Residents of Sai Mai district were told to evacuate to safer ground and Don Muang airport, location of the government's flood relief operations centre, was inundated.

"What we can do now is to manage it, so that it flows slowly, otherwise everybody will suffer," Yingluck told reporters, her voice trembling. "I haven't cried and I won't. I'll be strong to solve this problem for the Thai people. Right now we need to release floodwater to the sea as soon as possible and we need a quick rehabilitation plan."

The floods, caused in part by unusually heavy monsoon rain, have already killed 373 people in Thailand and disrupted the lives of nearly 2.5 million, until now mostly in the north and central provinces. The rains have also killed dozens in neighbouring Cambodia and Burma.

By Thursday night, floodwaters had overwhelmed seven of Bangkok's 50 districts, mostly on the northern outskirts. Roads became rivers, and homes and businesses were swamped. Relief agencies believe most if not all of the city could be flooded with waters rising between 20cm and 2 metres in the coming days. High tides this weekend are likely to place more pressure on the city's limited flood defences and could swell the Chao Phraya river to overflow flood barriers lining its banks. In the meantime, many people are remaining in their homes.

"The mayor of Bangkok has said that of the 140 evacuation centres that have been set up only a quarter are being used and none are full," Matt Cochrane, spokesman for the International Federation of the Red Cross in Bangkok, told the Guardian. "It is all about waiting and what is coming. This is the beginning of the potential humanitarian crisis for Bangkok. There is going to be water in most or all of the city. It won't be a tsunami, it is more likely to be a gradual rise."

Yingluck has warned the flood waters could stay for as long as a month. The Red Cross believes this will threaten a particular type of urban crisis in which public transport grinds to a halt, there are breaks in electricity leaving the city sweltering in 35C heat and 100% humidity, and the risks of mosquito-borne disease multiply.

And there are other dangers lurking in the waters. "When my father leaves to get food he makes sure he closes all the gates and doors - not to prevent intruders but to keep out the crocodiles," said Nara Rathnarathon, a resident in the north of the city. Thailand is reckoned to be the world's biggest breeder of crocodiles and scores are reported to have escaped from farms during the floods. Several have been killed or captured in residential areas in the ancient capital of Ayutthaya. Cochrane said parents had been told to keep children out of any gardens that remained dry because they could be safe havens for venomous snakes.

The economic impact is already being felt. At least seven huge industrial estates have already shut to the north of Bangkok, causing the central bank to revise down its growth forecast the economy from 4% to 3.1%.

Websites have posted instructions on the proper way to stack sandbags and residents have fortified homes with bricks, gypsum board and plastic sheets. Walls of sandbags or cinder blocks cover building entrances.

There has been panic buying in supermarkets, where bottled water is scarce, but many of the city's thousands of restaurants, bars and food stalls are operating as usual.

Nuntaporn Khorcharoen, whose home is next to the heavily inundated Bang Phlat district, told the Associated Press her family had stocked up and was staying put. "My father is adamant we have to stay to oversee the situation," the 30-year-old said. "He said even without electricity we will still have something to live on."

The defence ministry said 50,000 armed forces personnel were standing by with 1,000 boats and 1,000 vehicles to help evacuate people.

"We're considering whether we should order an evacuation of Tawee Wattana district as the flood situation there is worrying," said Bangkok's governor, Sukhumbhand Paribatra, after more water surged into Tawee Wattana canal.