The Metro Nashville Office of Emergency Management told local broadcaster News 2 that the parked RV exploded around 6.30am and damaged at least 20 surrounding buildings, including an AT&T office block which led to 911 communications and local flight control systems to be thrown into chaos.
Nashville Fire spokesman Joseph Pleasant said three people were taken to the hospital, though none were in critical condition.
CBS News reported that authorities found human remains near the blast site. It is unclear if the remains belong to someone in the RV or a victim of the blast.
The FBI has taken over the investigation, and asked the public to report any information they might have regarding the explosion. The Bureau of Alcohol Tobacco and Firearms as well as the Tennessee Bureau of Investigation are also aiding the investigation. Police dogs trained to sniff out accelerants are being used to search for other potential bombs.
The Tennessean reported that several people were taken to the department’s central precinct for questioning, but police have declined to provide further details regarding those individuals.
Nashville police announced that a 10-block radius of downtown streets would be closed as they investigate the scene further. A spokeswoman for the Metro Nashville Police Department said the site of the explosion was an “active scene.”
The police were called to check out a suspicious vehicle parked outside the AT&T office building - the city’s largest skyscraper - at 6am this morning, and called a hazardous devices unit to investigate.
Metro Police Spokesman Don Aaron said the police were originally called to the scene to investigate reports of gunfire. Though police did not find evidence of gunfire in the area, they did discover the RV, which prompted them to alert the bomb squad.
During a press briefing Friday morning, Police Chief John Drake said the officers responding to the RV heard it playing a recording “saying that a potential bomb would detonate within 15 minutes.”
Witnesses who were near the blast site told The Tennessean that they heard a recorded voice from the RV warning them to flee.
“Evacuate now. There is a bomb. A bomb is in this vehicle and will explode," the voice allegedly said.
After that, they said the RV began a 15-minute countdown.
The officers moved to evacuate the nearby apartment buildings and clear people from the streets.
Mr Aaron said officers went door-to-door before the explosion to evacuate residents who lived close to where the RV was parked. In the moments prior to the explosion, a woman’s voice calling for anyone who could hear the message to evacuate was played over loudspeakers in the area immediately around the RV.
Officers also apparently turned away a man who was walking his dog toward the RV just before it exploded.
The RV exploded at 6:30am. Authorities were unable to confirm if there was anyone inside the vehicle at the time of the explosion.
Noelle Ramussen told CBS News she was thankful for the officers for warning her and her family of the impending explosion, as the blast destroyed the front of her building.
"I'm so glad we left. I'm so glad we have our kids. And above anything else, I am so glad for those officers that walked into a building that they knew was a dangerous spot to be and, you know, woke us up and got us out. I'm so grateful," she said.
A Nashville resident, Bryan Norwood, told Forbes said he lives near the site of the explosion and heard gunfire this morning. Mr Norwood said the shots came in a series of bursts, and that the later rounds were loud enough to prompt him to barricade his door.
A man who lives nearby, Buck McCoy, posted a video to Facebook showing the aftermath of the explosion. His windows are completely blown out and water is pouring down from the ceiling of his home.
Alarms whir in the background, barely masking the cries of others whose Christmas mornings was ruined by the blast.
Black smoke billows into the air outside his home, rising from a vehicle fire on the ground outside.
“All my windows, every single one of them got blown into the next room. If I had been standing there it would have been horrible,” he told the Associated Press. “It felt like a bomb. It was that big,”
Mr McCoy also said he heard gunshots approximately 10 minutes before the explosion. He said he shoots recreationally and knows the difference between a gunshot and other loud popping noises.
John Cooper, the city’s mayor, told CNN that he was aware of the explosion and was on his way to the scene.
"I do know emergency services are calling in our help, all our specialties, to investigate the cause of the explosion and I'm sure more information will be posted soon," Mr Cooper said.
The explosion occurred in the heart of the city’s historic old town, which is home to its hospitality and tourist district.
The Nashville Convention & Visitors Corp is offering a $10,000 contribution toward a reward for anyone who can help law enforcement find the culprit.
Widespread AT&T outages were reported in the aftermath of the explosion.
A spokesman for the company said damage caused by the explosion disrupted service.
"Service for some customers in Nashville and the surrounding areas may be affected by damage to our facilities from the explosion this morning. We are in contact with law enforcement and working as quickly and safely as possible to restore service," the spokesman told The Tennessean.
The service disruption has also impacted several local police department’s 911 systems.
Flights out of the Nashville airport have been halted due to telecommunications issued caused by the outage.
A Department of Justice spokesperson said that it had been instructed to make “all DOJ resources available to assist in the investigation.”
Sen. Marsha Blackburn of Tennessee wrote in a tweet that she was “closely monitoring the situation.”
The state’s governor, Bill Lee, called for prayers and said the state would provide any resources needed by investigators to determine the cause of the explosion.
A press pool report confirmed that Joe Biden has been briefed on the situation.
"President-elect Biden has been briefed on the explosion in Nashville, TN. The president -elect and Dr. Biden thank all the first responders working today in response to the incident, and wish those who were injured a speedy recovery."
Donald Trump has also been briefed on the explosion, according to the deputy White House press secretary Judd Deere.
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