Bangkok, a sprawling city of more than 10 million people and criss-crossed by more than 1,000 canals, is between 1 and 1.5 metres (3 to 5 feet) above sea level and is sinking into its soft, loamy soil at an alarming rate, he said this week.

Smith, giving his scenario for Bangkok in 2025, is renowned in Thailand for controversial predictions.

He was dismissed as a crackpot for his tsunami warnings years before the 2004 Indian Ocean disaster which killed 5,395 Thais and foreign tourists on its Andaman Sea coast.

The problem, he says, is two-fold.

The city is subsiding at a rate of 10 cm (4 inches) per year, partly due to excessive pumping of underground water.

Global warming is causing seas to rise and there is evidence of severe coastal erosion just downstream from Bangkok.

His comments come as scientists and government officials from around the globe are meeting at a UN conference in Bangkok to work out ways to fight climate change and curb the growth of greenhouse gas emissions.

To avert disaster, Smith said, the city needed to construct a massive dyke to protect it from rising seas and increasingly violent storms.

"The system has to be started right now. Otherwise it will be too late to protect our capital city," he said.

FLOOD-FIGHTING NETWORK

As if to highlight the threat from flooding and bad weather, the capital has been hit by an unexpectedly early start to the rainy season. An intense storm has also caused widespread flooding in parts of southern and central Thailand.

Asked what was being done to avert disaster, Smith said: "The government does not pay any attention at all."

However, the Bangkok Metropolitan Administration says it has made flood control a top priority in recent years.

The BMA has more than 60 pumping stations and a network of water gates to regulate river and canal flows. Sewers and drains are regularly cleaned, waterways cleared of debris, and basins temporarily trap floodwaters.

Most Bangkok residents still remember the floods of 1995, among the the worst in decades.

Large areas of the capital were inundated as high tides on the Chao Phraya river, which runs through the city, collided with floodwaters flowing down from central areas of the country.

Rubbish-choked canals and drains were blamed for exacerbating the problem. Since then, the government has deployed prisoners to clear the canals and drains before the onset of the monsoon season.

However, Smith insists only a massive seawall would prevent his prediction of a paralysed city from coming true.