UPDATED: RV that exploded in Nashville broadcast message warning of imminent blast: Police

A recreational vehicle that exploded in downtown Nashville early Christmas morning broadcast a message over a loudspeaker that warned of an imminent blast just before a bomb detonated, according to a report.

The massive explosion destroyed storefronts, set cars on fire and scattered debris through the streets, sending at least three people to the hospital with noncritical injuries, police said.

In a video posted on social media, which The Washington Post said it had not yet verified, a voice can be heard saying, “This area must be evacuated now. If you can hear this message, evacuate now.”

"That was followed by the sounds of an explosion, and the video of the street scene turned to a blur," said The Post. Law enforcement officials in a midday news conference confirmed the early warning.

The Associated Press reported that the recorded message "said a potential bomb was to detonate in 15 minutes. Police evacuated nearby buildings and called in the bomb squad."

The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) are investigating.

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

"Officers first responded to the area after receiving a report of shots fired. They called in the bomb squad after seeing the suspicious vehicle, which later exploded," Fox News reported. "As of late Friday morning, police did not know if anyone had been inside the vehicle at the time of the explosion, and they were not yet able to confirm that shots were actually fired."

"Right now, it’s a public safety concern, to make sure everybody is accounted for and to make sure the spread of the fire doesn’t go any further," Michael Knight, a spokesman for the ATF in Nashville, told The AP.

A Philadelphia man staying in a nearby hotel told the AP he heard the blast. “It was a very loud explosion,” said Joseph Fafara. “We tried to rationalize it that it was an earthquake or something. But it was obvious it wasn’t an earthquake.”

"Black smoke and flames were seen early Friday billowing from the area, which is packed with bars, restaurants and other retail establishments and is known as the heart of downtown Nashville’s tourist scene," said the AP.

Social media was quickly loaded with first-hand accounts.

Mayor John Cooper also weighed in. "At 6:32 Christmas morning, @MNPDNashville and @NashvilleFD responded to the scene of an explosion on 2nd Ave, approximately one block north of Broadway. Metro Police confirm the source of the explosion came from a vehicle."

"The cause of the explosion is under investigation with help from federal authorities. MNPD will share updates as they become available and is restricting downtown traffic. Be safe Nashville. Thank you to our emergency personnel for your quick response."