The funnel was spotted by witnesses outside the state's biggest city, Birmingham, at about 5pm Central time, (2300 GMT) on Friday, and whipped through some of its neighborhoods.
"There does appear to be some significant damage," National Weather Service meteorologist Jody Aaron reported, adding that details were pretty sketchy.
Birmingham Police Lieutenant Sean Edwards said at least three people had been taken to hospital with minor injuries, but no reports of fatalities had been made.
The tornado left a path of destruction in its wake, with trees torn down and people trapped in damaged houses.
A confirmed, damaging tornado is moving through the south side of Birmingham, Alabama. Tornado warning continues: pic.twitter.com/J8zOxncJfD
โ The Weather Channel (@weatherchannel) December 25, 2015
Ruthie Green, resident of a working class neighborhood in downtown Birmingham, said she ran to a closet when a tornado warning came up on her iPad.
"Then I heard the big roaring, it didn't last more than three minutes," Green told AP. "I just laid down and just kept praying."
Fourteen people were previously reported killed and dozens injured by some two dozen tornadoes and uncharacteristic torrential rains, which hit Tennessee, Indiana and Mississippi in the past few days, the latter state bearing the brunt.
Comment: See also: 'Large & extremely dangerous': 7 dead in United States after 21 tornadoes sweep through South, Midwest regions