A motorhome exploded in downtown Nashville Friday, shattering windows and injuring three people in what police described as an "intentional act," as investigators searched for clues among scattered debris.
The blast in the southern US city left buildings and the road surface charred, as well as glass, tree branches and bricks strewn across the street in an area filled with businesses, restaurants and bars.
In a dramatic sequence of events that shattered the Christmas Day early morning peace, police were responding to calls that gunshots had been fired and arrived on the scene before the vehicle erupted in flames.
Their attention had been drawn to the "suspicious" motorhome in time for a bomb squad to clear the area before the explosion, police spokesman Don Aaron told reporters.
Pictures shared on social media from the immediate aftermath showed thick plumes of black smoke rising from the burning RV and store fronts that had been badly damaged.
US President Donald Trump was briefed on the incident, which is being investigated by the FBI and the US Bureau of Alcohol, Tobacco, Firearms and Explosives in addition to the metropolitan police.
Agents offered no possible motive immediately and made no link to any terrorism plot.
"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 blast was large enough to be felt several blocks away but the early hour -- 6:30 am (1130 GMT) -- meant streets were largely empty.
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."
Police said several people had been moved to a local station for questioning, although no arrests or details of suspects were announced.
US Senator Marsha Blackburn of Tennessee led messages of concern from multiple public figures, saying she was "praying for all those involved" and thanking the "brave first responders for keeping us safe."