A parked motor home exploded on a tree-lined street in downtown Nashville at dawn on Friday morning minutes after a recorded announcement emanating from the vehicle warned of a bomb, in what police said was an “intentional act” that injured at least three people.

Police said it was unclear whether anyone was inside the recreational vehicle at the time. CNN, citing unnamed sources, reported hours later that investigators had found possible human remains near the site of the explosion.

The Christmas Day blast, which rocked the heart of America’s country music capital, came just moments after officers responded to reports of gunfire in the area and discovered the recreational vehicle parked outside a downtown office tower.

Police heard a recorded voice warning that a “bomb would detonate in 15 minutes”, police said.

The message, as captured in a recording broadcast later by local television news stations, said: “This area must be evacuated now. This area must be evacuated now. If you can hear this message, evacuate now. If you can hear this message, evacuate now.”

Officers quickly went door-to-door in nearby buildings to hustle people to safety, and called for dispatch of the police bomb squad, which was on its way to the scene when the vehicle blew up, police spokesman Don Aaron said.

The Metro Nashville Police Department posted a photo of the recreational vehicle on its Twitter feed and said that the vehicle had arrived in the area at 1.22am (local time).

The blast ravaged the heart of the city, considered the capital of the US country music industry. It destroyed several other vehicles and severely damaged several buildings, sending a pall of black smoke into the sky that could be seen for miles.

Fire officials said three people were taken to local hospitals with minor injuries. Authorities said quick action by police to begin evacuating the area before the blast likely prevented more casualties.

“Obviously, they heard the announcements coming from this vehicle,” Aaron told reporters.

“They took them seriously. And worked to seal the streets to protect folks and we think it worked.” He called the blast “an intentional act”.