Seven-month-old twins are among at least 21 people killed and 50 reported missing after heavy flooding in parts of Tennessee.

A dispatcher at the Humphreys County Sheriff’s Office confirmed the number of those killed and missing and said authorities were working to conduct house-to-house searches of the area.

Record rainfall of up to 43 centimetres in some areas sparked massive flooding on Saturday afternoon and in the night (local time). Especially hard hit was the town of Waverly, about 88 kilometres west of Nashville. Hundreds of homes were left uninhabitable.

Waverly Mayor Wallace Frazier told the Tennessean newspaper that those killed in flooding ranged in age from babies to the elderly.

The Washington Post, citing family members, reported that seven-month-old twins died after they were swept from their father’s arms.

The twins’ grandmother Angie Willeby also told FOX 17 News that babies Ryan and Riliegh were swept away when flooding gripped Waverly on Saturday.

The flooding uprooted massive trees, tore through homes and tossed cars and pickup trucks into ditches and atop sheds and other structures.

Cindy Dunn, 48, told the Tennessean that she and her husband had been stranded in their attic for hours after floodwaters rose to 1.8 metres in their home. The pair were saved by a rescue crew that raised the bucket of a bulldozer up to a window they could get through.

“Hell. That’s what we had to go through,” Ms Dunn told the newspaper.

-with AAP