Preliminary figures from the National Weather Service showed that more than 50 tornadoes touched down throughout the eastern United States.
Most of those killed were in Tennessee, where 17 people died. Twelve others died in Alabama, five in Ohio, one in Pennsylvania and one in Mississippi.
One storm slammed into the town of Mossy Grove, in eastern Tennessee, cutting a path of destruction about a mile long and a mile wide, officials said.
Brenda Stansberry joined her husband in the basement of their Mossy Grove home only minutes before a tornado destroyed the house. When she came out, she said she was shocked to see the destruction.
"It's terrible," she said. "I don't know how to explain it. It's like a war zone or worse."
The storm hit during Sunday night services at the New Life Apostolic Church in Mossy Grove, badly damaging the church. The storm partially collapsed the building's roof and shattered glass, sending parishioners scrambling under pews for safety. No one in the church was injured.
David Gunther said he grabbed his 3-year-old daughter, jumped under a pew and started praying.
"When you have a child, you just want to protect them. That was my first instinct," he told CNN. "We got in the doors just in time."
Another congregation member, Kevin Davis, said simply, "We were just praying like we had never prayed before. ... God kept his hand on us."
Eight people were killed and 14 were unaccounted for in surrounding Morgan County, which is about 60 miles northwest of Knoxville, authorities said.
One of those killed was a volunteer firefighter, who suffered a heart attack while searching for survivors in the debris. Four others were killed in their car as they tried to outrun the storm.
Across the state, storms wreaked havoc, damaging or destroying hundreds of homes, uprooting trees and knocking down power lines. More than 80 people were injured.
"I don't remember ever having a two-day weather...