Bangkok , Thailand ( CNN ) -- Bangkok faces the highest flood levels yet and is preparing for the worst , the governor of the Thai capital told CNN . Residents are urged to flee the rising floodwaters , which have already forced the closure of Bangkok 's Don Muang airport and the evacuation of flood victims who have taken refuge there . Thailand 's government has declared a five-day public holiday in flood-affected provinces to try to encourage people to seek safety elsewhere before high tides expected this weekend . But Bangkok Gov . Sukhumbhand Paripatra told CNN the authorities could not evacuate a whole city and it was difficult to persuade the Thai people to leave their homes , despite the risk . CNNGo : Updated info for tourists . `` Apparently there will be large volume of water runoff coming toward the city tonight onwards , and over the weekend , '' he said . `` At the point of high tide , it will be very high , the highest this year . We are bracing for the worse . '' Thongthong Chantharangsu , a spokesman for Thailand 's Flood Relief Operations Center , appealed on TV for Bangkok residents to head to the countryside . Floodwaters extend from Rangsit , north of Bangkok , to Don Muang airport and Yingcharoen Market , state-run news agency MCOT reported . The water has reached 30cm ( 12 inches ) in places and is overflowing on to sidewalks and some roads , causing problems for small vehicles and leading to traffic congestion , the agency said . In a televised address Tuesday night , Thai Prime Minister Yingluck Shinawatra said the capital could be submerged by as much as 1.5 meters ( 4.9 feet ) of water . Of particular concern were areas along the Chao Phraya River , which winds through the capital and is expected to overwhelm embankments this weekend . The Airports of Thailand declared Don Muang airport , which primarily services domestic flights , closed Tuesday night , after floodwaters flowed onto runways and affected the lighting . Nok Air , which usually operates from Don Muang , was forced to cancel flights but should be able to run an almost normal schedule by Friday after moving its operations to the main Suvarnabhumi Airport , the airline 's chief executive Patee Sarasin said Wednesday . Some 3,000 Nok Air passengers were affected by flight cancellations Tuesday , he said . The flood relief operation will continue to be based at the airport , the Thai government said Wednesday . More than 600 prisoners held at Bang Kwang Central Prison have been evacuated , according to the Department of Corrections . The high-security prison has about 4,000 inmates , the chief of the prison said , some of them high-profile . The floods have also forced the Dusit Zoo to evacuate some animals , including goat antelope and Sika deer , to a zoo in the countryside , according to Dusit Zoo 's chief , Karnchai Saenwong . The U.S. ambassador to Thailand , Kristie A. Kenny , said the crisis was slow moving and it was hard to know what would be hit next . The United States has already provided civilian relief resources including water pumps , purifiers and life vests , she said , and two U.S. helicopters are helping the Thai military survey the extent of the flooding . Nationwide , the floods have killed 373 people and affected more than 9.5 million people , authorities said . The public holiday announced Tuesday will be from Thursday to next Monday and will be effective in 21 provinces , including Bangkok , that are still under water , a government spokeswoman said . The government has called the flooding the worst to afflict the nation in half a century and said it might take more than a month before the waters recede in some areas . The government has set up more than 1,700 shelters nationwide , and more than 113,000 people have taken refuge . Overall damage from the floods has risen and could top $ 6 billion , with the worst yet to come as the waters destroy shops and paralyze factories nationwide , the Thai Finance Ministry said . Thailand derives a significant portion of its revenue from tourism , which has been diminished by the flooding . CNN 's Elizabeth Yuan , Kocha Olarn and Paula Hancocks contributed to this report .
NEW : Bangkok 's governor warns of the highest water levels in next few days . These include 600 inmates at a prison , some animals from a zoo . He warns Bangkok could be submerged by as much as 1.5 meters ( 4.9 feet ) Authorities : Floods have killed two people and affected more than 9.5 million .