Thai officials say they can no longer hold back the floodwaters that are bearing down on the capital.

Prime Minister Yingluck Shinawatra, who is facing her first crisis since taking office in August, said Thursday she has ordered officials to open the city's floodgates and let the water pour through Bangkok's canals to the sea.

Officials say they are unsure whether water will overflow the canals into city streets, repeating the scenes of devastation already playing out in suburbs north of the capital.

But downtown shopkeepers such as Saowaluk Chaicharoenwattana are protecting their buildings with sandbags just in case.

The decision to open the floodgates has sparked a new rush to stock up on groceries and supplies, prompting officials to issue a warning against hoarding. Residents have also been ordered to remove vehicles from bridges and expressways.

On the northern edge of the city, water is already filling the streets as the flood surge from central Thailand strains against reinforced barriers. Several industrial estates have already been deluged, with the worst now expected in the next few days.

Bangkok resident Teemu Oittinen of Finland says he doubts that the barriers will hold.

Nationwide, the death toll after the worst floods in 50 years has risen to 320 with 9 million people affected. The floods have also affected Vietnam, Cambodia and Laos, killing hundreds more people in those countries.