Phitsanulok, Ayutthaya, Angthong, Kalasin, Surin, Si Sa Ket and Ubon Ratchathani were the hardest hit by Friday, but with reports coming in of flooding in Chon Buri.
Mr Chatchai said the tropical depression that brought the rain had now weakened, but a low-pressure system was still moving through the northeastern region. This was causing widespread rain, with particularly heavy downpours in the Northeast, East, Central Plains and Bangkok and nearby provinces.
Prime Minister Yingluck Shinawatra had ordered the Interior Ministry to assist people affected by the heavy rain and possible flash flooding on Friday and Saturday, he said.
The director-general said officials were monitoring weather conditions around the clock. Water pumps and other necessary equipment were ready to be delivered to high-risk flood areas near hillsides and waterways, if needed, he said.
Pratheep Keeratiraekha, governor of Si Sa Ket province, said all 22 districts were experiencing steady rain and this was expected to continue into Saturday. There was flood in several districts, including Kantharak, Khun Harn and Phu Sing. In Khun Han district around 100 villages and 10,000 rai of farm land were affected.
In Surin, the flood was said to be the worst for 40 years, with agricultural areas in 17 districts under water. The most severely affected were reported to be Muang, Sangkha, Si Narong, Sikhoraphum, Samrong Thap, Ratanaburi and Chom Phra districts.
Many areas in Muang district were reported to be under 30-50cm of water. Several communities, schools and government offices in the municipality were affected.
Highway No 24, a main road for travel to Si Sa Ket and Ubon Ratchathani, and to Bangkok, was also flooded in several spots by water running down from Phanom Dong Rak mountain.
In Nakhon Ratchasima, rain that began on Thursday evening was continuing as of noon Friday.
The Thung Samrit water reservoir in Pimai district was about full, so officials opened the water gate to release the water and allow space for more water from Lam Takong, Lam Chiang Klai and Lam Boriboon, that will flow to Pimai over the weekend.
In Muang district, many areas were flooded including streets around the Chatchai Hall Gymnasium, where the Asian Women's Volleyball Championship is under way.
Krisda Garden situated on Highway No 304 in tambon Pho Klang of Muang district was flooded after the wall at the back of the estate broke. The water spread into about 150 houses, rising to around one metre in less than an hour. Army trucks were helping evacuate residents.
In Ayutthaya, Udomsak Kaonoona, chief of the Disaster Prevention and Mitigation Provincial Office, said there was flooding fin three districts with 5,100 households affected.
Villagers in tambon Ban Krod and Ban Wa in Bang Pa-In district called on the province to urgently repair the road, which run parallel to the railway track, because this road helps prevent floodwaters from the Chao Phraya River flopwing to the east side of Bang Pa-in district, reports said.
In Chon Buri, heavy rain was reported since Thursday evening in Muang district. The Sukhumvit highway in Muang district was covered with water to a depth of 40-50cm height. Water was also reported on the way to Pattaya, with at least 10km affected, causing more traffic problems in the area.
In Bangkok, Governor Sukhumbhand Paribatra said there was no need for people to panic as there would be no flood crisis in the capital.
He said the Bangkok Metropolitan Administration (BMA) had prepared measures to counter any possible situation, particularly in all 37 flood-risk areas.
Adisak Khantee, director of the BMA's Drainage and Sewerage Department said water levels in various canals in Bang Khen, Lak Si and Don Muang were high due to the continued rainfall, but they there was no risk of an overflow.
The Chao Phraya river was flowing down from the North at 1,400 cubic metres per second, which was normal and no cause for concern, he added.
Prime Minister Yingluck on Friday morning visited San Seab Water Drainage Offce in Min Buri to observe the operation.
She was informed that the BMA can still handle the current water level by Wirat Meanchaiyanant, a member of the Bangkok Council for Min Buri district.