In Chai Nat's Noen Kham district, swift floodwaters severed roads, homes were flooded, agricultural areas including paddy fields and sugarcane plantations were damaged.
The forest runoff from the Phetchabun mountains flooded Ban Wang Daeng School in Phichit's Tap Khlo district, forcing the school to temporarily close.
Phang-nga authorities issued warning for small boats to keep ashore due to 2-3 metre waves and heavy rain was forecast.
In Thailand's former capital of Ayutthaya, Governor Witthaya Pewpong said rivers overflowed in eight districts, affecting much farmland although reservoirs could still receive more water from the North.
Sena district was hardest hit, while provincial officials tried their best to protect the provincial seat and historical sites from inundation, he said, adding that waters should recede if it does not rain again during the next few days.
In Prachinburi province, more than 700 male and female inmates will be relocated from Kabin Buri district prison which has been flooded.
The first group of 100 prisoners will be moved to Chanthaburi prison and the rest to Pathum Thani, said Somchai Premchai, Kabin Buri prison chief.
Water in the Prachin Buri River has been rising and has flooded structures on both sides of the waterway with the flood in Kabin Buri district seat measured at some 50cm.
In Suphan Buri province, water in the Tha Chin River spilled into the 100 Year Market – a provincial landmark -- while more pumps were installed and thousands of sandbags were laid to prevent flooding of significant commercial areas.
Ekaphan Inchaiua, Suphan Buri municipality mayor, said the flood followed several days of rainfall and water runoff from the North.
Residents along riverbanks were told last week to prepare to move their belongings to higher ground, and 18 water pumps have been installed, he said.
In the lower northern province of Nakhon Sawan, the commercial centre of Nong Bua district was flooded by 30cm of water, creating inconvenience to motorists.
Water was pumped out to nearby canals and rivers while sand bags were erected along Nong Bua and Chum Saeng roads.
Preecha Thongkam, Nakhon Sawan disaster chief, said flash flood and excessive water from the Phetchabun forests affected more than 200 households in the province.