Thai officials have warned millions of Bangkok residents to move their belongings to higher ground, as floodwaters began to inundate parts of the capital's outer districts.

Officials and witnesses said Friday water has risen to knee-level after seeping over canals in Bangkok's northern Lak-Si district, about 16 kilometers from the city center.

Many Bangkok residents are rushing to stock up on food and drinking water, while those in the flooded north have already fled their homes.

Thai Prime Minister Yingluck Shinawatra took steps to streamline flood relief operations by invoking special civil powers granted under the country's natural disaster law, following criticism of her government's handling of the crisis.

The move gives the prime minister full authority to prosecute officials if they fail to follow instructions.

Thailand's government said Friday 342 people have been killed in the floods, the worst the country has seen in decades.

Months of heavy monsoon rains have soaked large parts of Southeast Asia, forcing millions from their homes. Another 336 people have died in Cambodia, Laos and Vietnam.

On Thursday, the government ordered the opening of Bangkok's floodgates to drain water through the canals and relieve pressure on dikes that had kept water out of the city for several days.

Prime Minister Yingluck told the capital city to brace for floods, saying the government “cannot stop the water forever,” and that the canals running through the city to the Gulf of Thailand could overflow into the streets.