This order came after it was announced that the Hua Na Dam in Si Sa Ket province would increase its water drainage from 159 million cubic metres to 162 million cubic metres daily.
The Lam Pao Dam in Kalasin, meanwhile, has been draining water into the Chi River.
According to the Office of the National Water Resources announcement, the level of the Mun River is expected to rise by up to 113.50 metres compared to the mean sea level.
This will affect six districts, namely Mueang Ubon Ratchathani, Warin Chamrap, Phibun Mangsahan, Don Mot Daeng, Trakan Phuet Phon and Muang Sam Sip, the office said.
Some 436 households in 26 communities are shifting to 22 evacuation centres prepared by municipalities. The number of evacuees is expected to rise based on the rising water level.
Meanwhile, troops from the 22nd Military District are accelerating efforts to set up sandbag barriers in the Tha Kor Phai community to help residents shift their belongings to the evacuation centre.