A two-year-old girl survived a terrifying tornado that killed her parents and siblings at the weekend, US media reported, noting that she was in critical condition in hospital.

The unidentified toddler was found lying among the bodies of her family in a field near a flattened home in New Pekin, Indiana, said hospital staff.

"She continues to remain in critical condition," Cis Gruebbel, a nurse at Kosair Children's Hospital in Louisville, in neighboring Kentucky, told local media.

"The two-year-old lost her mum and dad, two-month old sister, and three-year-old brother in the storm last night."

The tornadoes have killed at least 37 people and injured hundreds, tearing across the US heartland and virtually wiping out communities.

Even as stunned Americans grappled with the magnitude of the destruction brought by Friday's twisters, the National Weather Service (NWS) issued new tornado warnings for parts of Georgia and Florida, in the country's southeast.

President Barack Obama called the governors of Indiana, Kentucky and Ohio to offer condolences for the dead and said the federal emergency management agency stood ready to help, the White House said.

Deaths were reported in Indiana, Kentucky, Ohio, Alabama and Georgia as the storm system moved eastward.