A huge blast tore through a section of downtown Nashville early Friday, after police responding to reports of gunfire discovered a parked motorhome blaring a warning that it carried a bomb.

The powerful explosion shattered windows and ripped apart trees, wounding several people when it detonated at 6:30 am (1230 GMT) in a section of the southern US city that was largely deserted due the early hour and the Christmas Day holiday.

Christmas explosion in Nashville
A Christmas Day explosion caused massive damage on a street in downtown Nashville Photo: Metro Nashville Police Department / Handout

Police chief John Drake told reporters there were no confirmed fatalities, but authorities were examining tissue found at the blast site that they believe could be human remains.

He added the city -- known as a hub for American country music -- had not received any threats, and a possible motive for the attack was unknown.

Nashville bombing
Nashville police are looking for witnesses and several people have been transferred to the police station for questioning Photo: Nashville Fire Department / Handout

The explosion could be felt miles away and damaged dozens of businesses -- scattering glass, debris and bricks as well as provoking the collapse of one building in an area with numerous bars, restaurants and shops.

In a dramatic sequence of events that shattered the Christmas morning calm, police rushed to the area after getting reports of gunshots and noticed the vehicle as they arrived on the scene.

A recorded message playing from the motorhome warned that a bomb would detonate within 15 minutes -- enough time for a bomb squad to clear the area before the explosion, Drake and police spokesman Don Aaron told reporters earlier Friday.

Nashville bombing
A bomb squad was able to clear people away from nearby surrounding before the blast Photo: Nashville Fire Department / Handout

Witnesses told the Tennessean newspaper the warning, spoken in a woman's voice, counted down to the blast.

"Evacuate now. There is a bomb. A bomb is in this vehicle and will explode," one recalled the chilling recording saying.

Map of the US state of Tennessee locating Nashville, hit by an explosion Friday. Photo: AFP / STAFF

Pictures shared on social media from the immediate aftermath showed thick plumes of black smoke rising from the burning RV and storefronts that had been torn apart.

The blast happened near an AT&T facility, knocking out phone service for many in the area. The telecommunications company said that "given the damage to our facility it will take time to restore service."

The Nashville International Airport announced it had temporarily halted flights due to "telecommunications issues" associated with the blast.

Nashville bombing
In this photo from the Twitter page of the Metro Nashville Police Department, a motorhome that later exploded in Nashville, Tennessee on December 25, 2020, is seen driving down a street Photo: Metro Nashville Police Department / Handout

Officers began knocking on doors and evacuating residents due the bomb warning, not knowing if or when the detonation could come.

A dog walker had been heading towards the vehicle just before the blast, the Tennessean newspaper said, but police turned him back, potentially saving him from serious injury or death.

The blast knocked an officer to the ground, the paper said, and gave another officer hearing loss.

Both President Donald Trump and President-elect Joe Biden were briefed on the incident, which is being investigated by the FBI and the US Bureau of Alcohol, Tobacco, Firearms and Explosives.

"This appears to have been an intentional act. Law enforcement is closing downtown streets as investigation continues," the Metro Nashville Police Department tweeted.

Firefighters said at least three people were taken to the hospital with minor injuries, according to local media.

The damage was "limited but it is dramatic," Nashville mayor John Cooper said, adding that the city was "lucky" the blast had occurred on Christmas when few people were downtown.

"It's unfortunate but any other morning I think it would have been a much worse story."

Biden issued a statement saying he and his wife Jill Biden "thank all the first responders working today in response to the incident, and wish those who were injured a speedy recovery."

Trump's spokesman Judd Deere tweeted that the president is "grateful for the incredible first responders and praying for those who were injured."

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