They rose by 1-8cm a day and would continue to increase rapidly, it said.
The Plain of Reeds covers the provinces of Long An, Tien Giang, and Dong Thap.
About 2,500ha of standing rice crop in Long An's Vinh Hung District are threatened by floods that have swollen to one metre.
Heavy rains and strong winds have flattened 2,000ha of rice in another district in the province, Moc Hoa.
In Dong Thap, normally one of the hardest hit during the annual flood season, the People's Committee has called a halt to the planting of the third rice crop in some areas in Tan Hong District since the floods have come early this year. Thousands of households in the province's upstream districts have been living in fear of river-bank erosion caused by flooding. Banks have been washed away at several spots since early this month.
In Hong Ngu District, some 1,5000 households need to be moved out of vulnerable areas, according to the local Infrastructure Economy Bureau.
Nguyen Van Lich, deputy chairman of the Thuong Phuoc Commune People's Committee in Hong Ngu District, said erosion threatened around six kilometres of river banks, requiring 500 households to be moved out.
Current regulations require households living within 30m of eroded river banks to relocate immediately, but the commune now has 53 households living within 5-15 meters of eroded banks.Lich said they were too poor to afford a move.
The Dong Thap People's Committee has instructed the Department of Culture, Sport and Tourism to teach children between the ages of seven and 15 swimming to prevent drowning during the flood season.
Under the programme, swimming classes will be held for more than 20,000 children.
Dong Thap has targeted introducing swimming lessons as extracurricular activity at 18 per cent of primary and secondary schools by 2015.
The flood levels in the Tien and Hau, two major tributaries of the Mekong, could peak at the end of September and early October, according to the Centre for Hydro-Meteorological Forecasting.
The floods could reach the third and highest warning level, but would still be lower than last year when there was record flooding, the centre said.
However, this year's levels could be higher than the average level of the past many years, it warned.
(VietNamNet/Viet Nam News)