Thailand is counting the multibillion-dollar cost of nationwide flooding that has killed nearly 270 people and may yet cause more havoc as waters threaten to engulf the country's capital.

Bank of Thailand governor Prasarn Trairatvorakul said a preliminary estimate by the central bank shows economic losses from flooding that began in late July range from $1.9 billion to $2.6 billion US.

That figure doesn't include damages to assets or reconstruction costs and is expected to rise as the floodwaters surge toward Bangkok, a city of about 10 million people. Some of its outlying areas are already under water.

Prime Minister Yingluck Shinawatra and Bangkok officials pleaded Tuesday with the city's residents not to panic as workers raced to complete three critical flood walls with only one or two days to go before the already swollen river that winds through the capital bursts its banks.

Supermarket shelves have been cleared by shoppers of basic items such as rice, bottled water, pork and chicken. Flood damage to agricultural land in the country's north is expected to push up food prices, rice in particular.

The disaster is a further blow to Thailand's electronics and auto industries, which have only just recovered from the production disruptions caused by the March 11 tsunami in Japan that knocked out suppliers of critical components. A dive in Thailand's auto production caused the economy to shrink in the second quarter.

A man casts a fishing net in a flooded area in Ayutthaya province on Monday. REUTERS/Chaiwat Subprasom

The flooding is the worst to hit the Southeast Asian nation in decades. About 8.2 million people in 60 of Thailand's 77 provinces have been affected by floods and mudslides, and 30 provinces are currently inundated. Prolonged monsoon flooding, typhoons and storms have killed hundreds of people across Southeast Asia, China, Japan and South Asia in the last four months.

Moody's Analytics economist Fred Gibson said economic losses from the flooding could swell if it spreads to the eastern seaboard province of Rayong where two thirds of Thai industry is located.

Honda Motor Co. said its Thai vehicle production has been suspended after two industrial estates in the historic capital of Ayutthaya, north of Bangkok, were inundated. Local media reported that hundreds of new Honda cars were submerged.

Officials at the Agriculture Ministry said 1.17 million hectares of rice fields might be damaged. Thailand, the world's biggest rice exporter, has about 10.9 million hectares planted with the staple grain.

Another 283,279 hectares of land planted with other crops is also likely to have suffered damage, the ministry said.