Smoke was seen rising above the city centre after the explosion at about 06:30 (00:30 GMT) on Friday.
However, Nashville authorities later confirmed the blast was an "intentional act", triggered by a parked vehicle.
Residents from as far away as Brentwood reported feeling and hearing the blast.
On arrival, they discovered a recreational vehicle blaring a message that warned people to evacuate the area so they began to evacuate nearby buildings. Several police agencies reported that their 911 systems were down because of the outage, including Murfreesboro and Knox County, home to Knoxville about 180 miles (290 kilometers) east of Nashville.
Small fires broke out on the debris-filled streets as alarms sounded.
"Initial evidence does show that the early morning explosion was a deliberate bomb set off in our community and the blast caused injuries and catastrophic damage to this very historic part of Nashville", Nashville Mayor John Cooper said.
Officers went door to door, telling residents to evacuate, even turning around one man who was out walking his dog, Aaron said.
'The explosion was significant as you can see from the street.
Chas Sisk, senior editor for member station WPLN in Nashville, joins us with the latest. Much of downtown remains shut down. Federal investigators from the Bureau of Alcohol, Tobacco, Firearms and Explosives were also on the scene.
Instead, they "encountered" what police are calling a suspicious vehicle, and called the bomb squad. There are now no suspects and police have no idea what the motive could have been. "As soon as COVID hit, even they said, "Nope, don't want to touch it.' So, Ott looks for creative solutions for clients who can't buy outright."I actually drive them to go talk to a Realtor and buy a piece of property".
The explosion occurred about two blocks from Lower Broadway, where Nashville's famous live music venues are located.
The Nashville Fire Department evacuated the downtown riverfront, according to WPLN, and later responded to a building that reportedly caught fire.
Windows are blown out in a building near the scene of an explosion in downtown Nashville, Tenn., Friday, Dec. 25, 2020.
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