Peak tides are continuing to test Bangkok's flood defences as Thailand's prime minister expressed optimism that the country's worst flooding in a half-century would mostly spare the Thai capital.

At least two more areas of the city were flooded on Sunday as coastal high tides pushed up the main Chao Phraya river from the Gulf of Thailand, but the city's defences otherwise have held firm during a weekend of critical water masses, officials say.

Sukhumbhand Paribatra, Bangkok's governor, said the Chao Phraya had reached a record level early on Sunday of 2.53 metres, topping 2.5-metre flood barriers. However, the tides were expected to ease below critical levels after Monday, and officials have suggested that the flooding situation will improve after that.

Prime Minister Yingluck Shinawatra said the city's fate rested its network of defences and sandbag walls.

"It depends on the level of the sea and sometimes it's about the stability of the way we put the sandbags," she told
reporters. "Hopefully, the sandbags are quite strong enough. So if the sandbags don't fall over, it should be OK."

She said people should not lose confidence in Bangkok: "We will recover soon."

Tens of thousands of people fled the capital ahead of the high tides. 

Disease fears

While downtown Bangkok was bone-dry, areas along the city's outskirts saw flooding spread. Provinces just north of the Bangkok, such as Pathun Thani and Ayutthaya, have been largely inundated for weeks.

Fears about water-borne diseases and malaria are growing and aid workers warned that many people were living in floodwater without access to food and water.

Al Jazeera's Aela Callen, reporting from Bangkok, said the situation would remain precarious for "several weeks" and that additional challenges are still ahead.

"All eyes will be on how the government focuses on the recovery effort," Callen said. "The government doesn't want to make people feel like they have been forgotten."

The floods follow unusually heavy monsoon rain. But there have also been accusations that authorities mistakenly delayed releasing water from dams early in the rainy season. By the time they had to release it, rain was heavy and
rivers full.

Floods in Thailand have killed about 380 people since mid-July and are estimated to have disrupted the lives of nearly 2.2 million people over the past few months.

The governor of the Bank of Thailand recently estimated economic losses to be as high as $2.6bn. Hundreds of factories have been forced to close and a lot of the country's rice crops have been destroyed.