This riverside administration office in Nakhon Phanom has been overwhelmed by the Mekong River, which continues to rise as heavy rain pounds the Northeast. (Photo via Twitter/@News1005fm)

Provinces along the Mekong River have been warned of possible flooding due to the rapidly rising water level of the river.

Heavy rain continued in several parts of the country Sunday, triggering more flooding incidents.

In the northeastern province of Sakon Nakhon, for instance, several parts of Phon Na Kaeo district were flooded by water overflowing some major creeks.

Several villages in tabmon Natong Watthana were covered Sunday with flood water about 1m deep as water was overflowing Huay Tong creek in the area.

Naring Phrommuang, 70, a flood victim in Ban Natong Noi, said evacuations were carried out Sunday following flooding incidents at this and other villages in the tambon.

Red flags were put up in Muang district warning people of the possible overflow of Nong Han Lake. The city was severely damaged by floods in July last year. Northeastern provinces along the Mekong River, in particular, were being warned of possible flooding due as water levels in the river rose.

The hydrology office in Nong Khai said heavy rains in northern Thailand and Laos were pouring water into the Mekong River and downstream provinces were likely to flood.

Provincial authorities said the water is threatening to overflow river banks in Nong Khai, Nakhon Phanom and Ubon Ratchathani.

The regional office of the National Water Resources Board in Ubon Ratchathani pointed to Khong Chiam as a district at critical risk of the river bursting its banks. Residents along the Mekong in Khong Chiam are urged to move to higher ground, it added.

Mukdahan also saw a rapid rise in water levels in the Mekong River, which late Sunday afternoon almost reached the "crisis" level of 12.5m, which will result in an overflow, a source said.

As of 3pm, the highest level measured was 12.04m, said the source, adding the province was closely monitoring the water level in the river and would issue a flood warning as soon as the water reaches the crisis level.

A similar water situation in the river was also reported in Nakhon Phanom where seven districts have already been declared flood-affected zones, following continual heavy rain over the previous three days. Residents in the northern province of Chiang Rai have also received a severe weather warning.

The Department of Disaster Prevention and Mitigation, however, said the overall flooding situation, affecting more than 11,160 people in close to 4,200 households in 32 districts of 20 provinces, was improving.

Tropical storm Son Tinh had from July 17 until July 23 triggered flash floods and landslides in these provinces, said Chayaphol Thitisak, director-general of the department.

But while most of the affected provinces were recovering, cleaning up and repairing damage left after those incidents, a major landslide erupted in Ban Huay Khab in Bo Kleu district of Nan province on Saturday claiming eight lives. About 100 more villagers were evacuated to a temporary shelter after the incident, he said.

Meanwhile, four districts downstream of the almost full Vajiralongkorn dam in Kanchanaburi are being warned of possible rises in the volume of excess water needed to be drained off the dam.

The level in the dam has now reached a two-decade high.

Provincial governor Jirakiat Phumsawas warned the districts of Thong Pha Phum, Sai Yok, Tha Muang and Tha Maka that the dam would have to increase its water release rate due to a steady rise in its water level.