Residents of the Thai capital Bangkok have cleared supermarket shelves of food and water as they brace for flood waters to reach the city in the coming days.

One cashier said his store's shelves were almost empty Wednesday, as customers stocked up on rice, instant noodles and other non-perishable items.

Thai Prime Minister Yingluck Shinawatra urged businesses not to take advantage of panic buying to raise prices. Her government has been racing to reinforce flood barriers and dig new canals on the capital's outskirts to protect it from flood waters streaming from the country's north.

The floods already have submerged the city of Ayutthaya, home to ancient temples just north of Bangkok. Rescue workers have been plucking stranded residents from one-story high waters and handing out food supplies.

Floods have submerged one third of Thailand's 77 provinces and killed at least 281 people since late July. The floods also have ruined Thai rice fields and shut down the production facilities of automakers and high-tech companies.

Thailand and other Asian nations have been battered by months of monsoon rains and typhoons that have killed hundreds of people and caused billions of dollars of damage.