Official sources said Collectors of Theni and Idukki districts had been alerted about the flood warning.
The water level in the Mullaperiyar dam, over which Tamil Nadu and Kerala are at loggerheads, touched 140.1 feet against its maximum level of 142 feet. The inflow was 1,947 cusecs and discharge 900 cusecs, they said.
They said PWD engineers from Kerala also visited the dam site for an inspection.
The Supreme Court had allowed Tamil Nadu to raise the level to 142 feet overruling Kerala's objections to raise the level beyond 136 feet, citing safety reasons.