VIDEO: Reuters BC-ASIA-OCT07-THAILAND-F, ASIA: STORY 5268AS

Thailand's prime minister says the nation is in a serious flood crisis and the capital Bangkok will be affected.

Yingluck Shinawatra said Friday in a televised address that 252 people have died across the country due to more than two months of heavy rains. She warned that major flooding is going to directly affect Bangkok.

Thai authorities raced to put up flood walls alongside canals and rivers on Bangkok's northern outskirts as huge amounts of muddy water flow down river.

Efforts have been made to protect ancient monuments and key industrial areas. The military has been deployed to help victims and army camps are being opened to evacuees.

Surging waters are threatening a U.N. World Heritage site in the ancient city of Ayutthaya, and officials worry the centuries-old Chaiwattanaram temple there could suffer permanent damage. UNESCO officials in Bangkok say they may request emergency assistance for the ancient city.

Thai weather forecasters say more rains are expected in the coming days, and the situation is likely to get worse.

Torrential rains and floods have also killed 150 people in Cambodia and southern Vietnam, and about 60 people in the Philippines. Millions of people in the Asia-Pacific region have been displaced.

U.S. Secretary of State Hillary Rodham Clinton has sent condolences on behalf of President Obama and the American people to all those who have lost family and loved ones in the floods in Thailand, Cambodia, Laos, Vietnam and the Philippines.