Thailand has bolstered flood defences at Bangkok's main airport and other areas as it works to shield the city of 12 million people from the worst inundation in decades, officials said Tuesday.

Flood protection walls have been raised to a height of up to 3.5 metres (11.5 feet) at Suvarnabhumi, the country's main air hub, Airports of Thailand (AOT) acting director Somchai Sawasdipol told AFP.

He said the airport would continue to operate normally.

"I am confident (that we can prevent floods at Suvarnabhumi) but we will not be careless," Somchai said, adding that the airport had two major water pumping stations and a 24-hour team to monitor the situation.

At least 269 people have died in more than two months of floods that have damaged the homes and livelihoods of millions of people, according to the government. More than 200 people have died in neighbouring Cambodia.

Thai Prime Minister Yingluck Shinawatra told a cabinet meeting that "the flood situation is serious, more than a tsunami because a tsunami comes and goes but floods last longer," government spokeswoman Titima Chaisaeng said.

The authorities have been building new flood walls in several locations in the north and east of the low-lying capital, where many residents were stocking up on sandbags, non-perishable food and other essential items.

Massive efforts are under way to stop the waters reaching the sprawling city, which has so far escaped serious flooding, unlike areas just north of the capital, which have seen water up to several metres deep.

A major industrial park home to companies including Japanese automaker Honda has been inundated.

A large amount of run-off water is expected to reach Bangkok in mid-October, while high tides will make it harder for the floods to flow out to sea.

"Whether we can protect Bangkok depends on three factors -- rain levels, run-off water from upcountry and the high tide," said Justice Minister Pracha Promnog, who heads the government's flood relief centre.

"The government will try its best, but no one can say what will happen. We will try to divert as much water into the sea as we can."

With the notable exception of the ancient city of Ayutthaya just north of Bangkok, where historic temples are partially under water, the country's top tourist destinations are mostly outside the worst affected areas.

Some foreign governments, including Australia, nevertheless warned their nationals to exercise caution.

Thailand's tourism minister said the disaster might lead to a dip in foreign visitor arrivals, along with the effect of the European debt crisis, but would not have a lasting impact.

"It may be affected by 10 to 20 percent but we will try to keep our target of 19 million visitors" this year, Chumpol Silapa-archa told reporters.

The cabinet agreed to earmark 10 percent of every ministry's budget, totalling about 80 billion baht, for flood relief. China, the United States, New Zealand and Japan have donated money and equipment to tackle the crisis.