Torrential rain is forecast in the southern region of the country over the next two days, the weather agency warned on Thursday, as flooding caused major disruptions in Phuket.
In its latest alert, the Meteorological Department urged people in the region to be prepared for downpours on Friday and Saturday.
Northeastern provinces can expect rain during the same period due to an impact from depression Nesat as it was moving northeastward in northern Vietnam, the weather agency said.
The chance of rain in Phuket would be 70% on Friday and Saturday, it added.
Phuket has been under water since Sunday and workers are deploying more sandbangs to defend downtown areas from flooding that could inflict damage on businesses.
Multiple landslides caused by torrential rain blocked traffic and caused blackouts on the tourist island on Thursday, but its airport remained open.
Three reservoirs on the island are filled beyond their capacity. Provincial authorities had been hoping for a respite from rain to give the local irrigation office a chance to discharge more water.
Floods have ravaged 28 provinces so far, with Ubon Ratchathani among the worst hit with some areas inundated since mid-August and water showing no signs of receding, according to the Disaster Prevention and Mitigation Department.