The floods have hit 15 provinces in the Northeast, Central and eastern regions, including Ubon Ratchathani, Surin, Si Sa Ket, Ayutthaya, Nakhon Sawan, Prachin Buri and Sa Kaeo.
As water levels in some major rivers continue to rise and with more rainfall expected this week, riverside residentsSunday were told to move their belongings to higher ground.
In Suphan Buri province, local authorities prepared about 100,000 sandbags and installed water pumps to safeguard the city centre in case the Tha Chin River overflows.
In Pathum Thani, residents on the banks of the Chao Phraya River in Sam Khok district moved their cars to higher ground and prepared boats in case they had to evacuate.
Public Health Minister Pradit Sinthawanarong yesterday ordered staff at hospitals in low-lying areas of Lop Buri province to move medical equipment to higher floors and make sure reserve power systems are working.
Earlier, the Meteorology Department forecast increasing rainfall in the lower North, Central and Northeastern provinces between Wednesday and Saturday when a monsoon is expected to arrive.
This is the second time the country has gone on flood alert in a week. A depression last week caused flooding in eight provinces, affecting tens of thousands of homes.
Thai Airways International and Air Asia yesterday cancelled or postponed a number of flights to Hong Kong due to the impact of Typhoon Usagi, which moved past Thailand last week.
Ms Yingluck yesterday ordered disaster relief units under the armed forces to work with provincial disaster prevention and mitigation offices to help flood-hit residents in 15 provinces.
Col Thanathip Sawangsaeng, the defence spokesman, said relief units under the ministry have sent 1,500 soldiers, 35 trucks, five excavators and 29 flat-bottom boats to troubled areas.
Floods have also hit the Kabin Buri district of Prachin Buri province hard, forcing 734 inmates at Kabin Buri prison to be relocated.
Somchai Premjai, the Kabin Buri prison commander, said he had sought permission from the Zone 2 Corrections Office in Chon Buri to relocate the inmates to Sa Kaeo and Chanthaburi prisons. By noon on Sunday, the prison was 20cm under water.
In the municipal area, the water level in the Kabin Buri municipal market had reached one metre. Nearly all roads in the municipality have been flooded.
Deputy Prime Minister Plodprasop Suraswadi said he was confident the country would not face a repeat of 2011 floods, as the water mass in the Chao Phraya basin is still at manageable levels.