Rescuers scouring a muddy field littered with debris on Thursday thought they had found a doll lying face-down in the mud. Then it moved.

In a grassy pasture strewn with toys, splintered lumber and bricks, 11-month-old Kyson lay 150m from where his home once stood.

The man who found the baby at first thought that he was a doll. 'As soon as I saw his little butt cheeks move I hollered, 'It's not a baby doll. It's alive!'' said firefighter David Harmon, who had been looking for survivors of the deadliest tornado rampage in the US in two decades.

The field had already been combed once by rescuers, and finding anyone alive in the devastation seemed improbable.

The body of Kyson's mother, 24-year-old Kerri Stowell, was found in the same field, and there was no sign of their home.

Kyson's survival was a story of hope amid the misery caused by tornadoes across the states of Tennessee, Kentucky, Mississippi, Alabama and Arkansas.

At a makeshift shelter for victims, Reverend Doyle Farris said the baby was a reminder that people 'should never give up, even in the midst of the worst storm'.

The boy's grandfather Doug Stowell said it was at least two hours after the storm before his grandson was found.

The baby had scrapes and gashes on his cheek and by his big blue eyes, but otherwise was fine.

'He's just a miracle,' Mr Stowell said. The boy will now be raised by his grandparents.

Tuesday's weather produced one of the 15 worst tornado death tolls since 1950, and the nation's deadliest barrage of tornadoes since 1985, when 76 people died.

ASSOCIATED PRESS