Tropical storm Podul has ravaged several provinces in the North and Northeast regions, with Khon Kaen the hardest hit.
The flooding in Khon Kaen province was reported to be as high as three metres in some parts of the province.
Non Sawang and Non Sa-ard communities in tambon Nai Muang of Ban Phai district were some of the most heavily affected parts of the province, with over 1,000 houses hit.
Residents were stranded on their roofs, while those who escaped the floods in time crowded local roads and waited for help from authorities as their houses were submerged overnight.
In addition to homes, many vehicles were submerged under the strong currents.
Suparb Maungsri, 57, of Non Sa-ard, said the floodwater had been rising since 8pm on Friday. As of 10am on Saturday, they still had not received any help.
"This year, the flooded area has expanded, making the deluge the biggest in 40 years," he lamented.
"My family members and our neighbours have to stay on the roof. We urgently need help. Boats should be brought over to take people to stay at Wat Chanprasit in Ban Pai municipality," he added.
In northeastern Roi Et province, three dykes north of Lampao dam collapsed, inundating tens of thousands of rai of rice fields, farmland and residential areas.
The situation was aggravated by run-off, which converged in Lam Nam Yung in tambon Wang Luang of Selephum district.
In Muang district, the floodwater was 60-90cm high, and soldiers were deployed to help people move their belongings.
A section of a road also collapsed due to torrential currents in Selaphum district. Heavy machinery was sent by a military rescue team to alleviate the situation.
In adjacent Kalasin province, heavy downpours caused the Huay Sithon reservoir to overflow, engulfing 10 communities in the centre of Muang district.
About 450 households were affected, with water reaching chest-high level. In some areas, there was more than a metre of flooding.
Kalasin governor Kraisorn Kongchalard tried to quell fears of flooding that could be caused by a dam overflow, as heavy rain continued to pound the district.
Governor Kraisorn told media the Lampao dam can still take more water.
The dam is now holding 719 million cubic metres of water, or about 41% of its capacity.
Royal Irrigation Department (RID) director-general Thongplew Kongjun said the agency deployed 15 large water pumps and eight water-propelling machines to divert water from the overflowing reservoir in Kalasin and collapsed dykes in Roi Et province.
Torrential rain caused by Podul led to runoff-induced landslides in mountainous areas such as Nan province. The avalanche of rain-soaked soils rolled down and hit 14 houses in Ban Huay Mon in tahmbon Santa in Na Noi district.
Four houses were seriously damaged, while the landslides blocked local roads, disrupting outside relief efforts.
Phrae provincial governor Phongrath Piromrad ordered officials to prepare for evacuation and relief efforts after rain pounded the province for 24 consecutive hours.
Located in a mountainous area, the province is facing massive run-off and forest mudslides.
The water levels in the Yom River and the connected small canals are also rising.
Twenty-three highways across 12 provinces were overflowing due to tropical storm Podul. Some of the routes are currently unusable, said Department of Highways (DoH) director-general Anon Luangboriboon.
The most affected route is a section of Highway 2 which passes through Phon district in Khon Kaen. Water reached the metre-high mark at the 239-294 milestone of the highway, which was not passable on Saturday.
Highway 212 at milestone 510 in Amnat Charoen district is also unusable, as water levels were higher than 60cm on Saturday and continuing to rise.
He urged motorists to call the DoH Hotline at 1586 to check the highway conditions in the flood-hit provinces.
Worawut Mala, director of the State Railway of Thailand (SRT), said train services and railways in 12 of the severely flood-hit areas are still operating and not affected by the floods.
The Meteorological Department has warned that heavy rain will continue until late Sunday.
The weather forecasting agency warned 27 provinces in the North, Central Plains, East and South to remain vigilant. The agency said waves are expected to be between two and four metres high in the Andaman Sea and the upper Gulf of Thailand.
All ships should proceed with caution. Small boats have been advised to remain ashore during the period.
Storm closes waterfall
Thung Salaeng Luang National Park authorities have closed three popular attractions until conditions return to normal, after flash floods and forest runoff triggered by tropical storm Podul made it dangerous to visit the sites.
On its Facebook page, the national park announced the rope bridge, Kaeng Sopha waterfall (both in Nakhon Thai district of Phitsanulok) and Thung Salaeng Luang (also called Nong Mae Na in Khao Kho district of Phetchabun) would be closed to visitors as forest runoff had inundated the areas.
Two caves inside the national parks -- Tham Duan-Dao and Tham Phra Wang Daeng in Noen Maprang district of Phitsanulok -- were also hit by flooding, said the Facebook administrator.
Many parts of the country are now on high alert for more heavy rain and flooding from Podul, with the Northeast region the hardest hit so far since the heavy rains began.