The Chao Phraya barrage is accelerating its discharge of water which is building up rapidly from downpours in upstream northern provinces.
The heavy discharge, at 1,423 cubic metres of water per second on Wednesday and rising, threatens to swamp the low-lying Chaiyo, Muang and Pa Mok districts downstream, in the rice-belt Ang Thong province, according to the province's disaster prevention and mitigation office.
The release of water by the barrage in Chai Nat, one of the country's most strategic water diversion points, was being closely monitored.
Prime Minister Prayut Chan-o-cha, accompanied by Interior Minister Anupong Paojinda, travelled by helicopter to Chai Nat to inspect the barrage's flood mitigation capacity and assess the overall flood-fighting plan in the lower Chao Phraya region.
Persistent heavy rainfall in the North has sent water surging, setting off flood alarms in nearby provinces.
On Wednesday, Ang Thong's disaster prevention and mitigation office advised residents in riverfront communities along the Chao Phraya and its tributary Noi River in Chaiyo, Muang and Pa Mok districts to move their belongings to higher ground in anticipation of a rapid surge of water.
Freight barges were also warned to navigate carefully as the Chao Phraya River is a busy transport route, and could be hit by the increasingly strong current, according to office head Supeeporn Mora.
During his tour of Chai Nat on Wednesday, Gen Prayut said he had been briefed on water management issues and impediments in implementing flood alleviation policies.
"The government is concerned that more provinces are being hit by the floods. We need to find a way to beat it and find a solution," he said.
The Office of the National Water Resources has devised water management plans for dealing with such problems.
The prime minister said he has stressed the need to remove debris in the waterways to help speed up drainage of excess water.
At the same time, a plan must be drawn to store water to be supplied to farmland outside of the irrigation areas.
In the northeastern province of Loei, heavy downpours on Tuesday night triggered widespread floods.