A day earlier the 226-meter stretch of dam breached at Dongting Lake in Hunan province, with 5,700 residents relocated, China Central Television reported.
More than 2,300 rescue personnel were working to build a second line of defense, with footage showing excavators piling boulders into barriers and being resupplied by trucks.
No one had been harmed as of early Saturday, reports said.
Earlier footage showed a wave of water surging through a breach in the dike past several overturned lorries, along with large stretches of half-submerged houses and fields in the surrounding area.
On Saturday afternoon the Ministry of Water Resources said it would also inspect dams on Poyang lake, China’s largest freshwater lake, in southeastern China, as well as embankments along the lower reaches of the Yangtze River.
Heavy rainfall pounded parts Hunan province earlier this week, causing the Miluo River in Pingjiang county to swell to its highest in 70 years.
Local authorities responded by activating the maximum emergency response level. State media showed large parts of towns waterlogged and stranded people being rescued on boats.