Downtown Nashville was sealed off on Friday, after a large explosion destroyed several buildings on Christmas morning in what local police said was an “intentional act”.

Nashville mayor John Cooper said: “Initial evidence does show that it was a deliberate bomb being set off in our community.”

At a briefing late morning, the FBI announced that the agency, along with the Bureau of Alcohol, Tobacco, Firearms and Explosives, would lead the investigation into a blast that left three people with non-critical injuries.

Law enforcement officials in Tennessee’s largest city told multiple media outlets that authorities had also found possible human remains in the vicinity of the explosion. It was unclear how the remains were related to the incident or whether they might belong to someone responsible.

Authorities said they had received a phone call warning that a parked recreational vehicle (RV) was set to explode in 15 minutes. The RV itself began broadcasting an apparently recorded repeating message for anyone nearby to stand away.

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.”

As Nashville police officers cleared the area of residents, the vehicle exploded, causing structural damage to several buildings, knocking down trees, and smashing windows for hundreds of yards.

“We had one officer that was knocked to the ground … and we are currently sweeping the area to make sure everyone is safe,” said a Nashville police spokesman, Don Aaron.

Aaron said police are not aware of other threats to public, but bomb dogs swept the area as a precaution. Authorities could not say if anyone was in the vehicle when it exploded.

Don Cochran, US attorney for Nashville, said the Department of Justice was directing its full resources to the investigation. FBI assistant special agent Matt Foster appealed to the public for tips. “We need your leads and we need your help,” he said.

Nashville police tweeted out a picture of the suspected vehicle caught on a security camera, saying it had arrived in the area at approximately 1.22am local time. It appeared to be a relatively old model with a pale paint job.

The ATF special agent in charge, Mickey French, said the agency had activated a national response team, including explosives experts to help investigate the incident. “Our main priority is obviously to keep our citizens safe and secure,” he said.

Images from the city’s entertainment district showed multiple buildings with windows blown out and masonry and rubble scattered in the street, and several burnt-out vehicles. Earlier images showed flames and smoke, and what appeared to be the charred remains of the RV.

Donald Trump has been briefed, according to the White House spokesman Judd Deere, who said that the president, who is spending the holidays in Florida, will continue to receive regular updates. The US justice department said the acting attorney general, Jeff Rosen, was also briefed and directed all department resources be made available to help with the investigation.

According to reports in the Tennessean, the blast was felt for miles and triggered a response from a police bomb squad as well as firefighters and other state and federal law enforcement officials.

“The explosion was significant, as you can see, the police department, its federal partners – the FBI and ATF – are conducting a large-scale investigation to this point,” said Nashville’s police spokesman. “We do believe that the explosion was an intentional act.”

Police later said the incident was linked to a vehicle parked outside a fondue restaurant, the Melting Pot.

The owner of the nearby Nashville Downtown hostel told the paper guests were evacuated to Nissan Stadium for shelter. He said he got a call early on Friday from his staff reporting hearing a “loud boom” and the fire alarm going off.

Nashville’s mayor, John Cooper, urged people to stay away from the downtown area, as police and federal authorities launched their investigation. Cooper said the city was lucky that the number of injuries was limited.

Governor Bill Lee of Tennessee said on Twitter that the state would provide the resources necessary “to determine what happened and who was responsible”.

Andrew McCabe, a former deputy FBI director, told CNN that an explosion of this size would be investigated as a possible act of terrorism. He said it was possible police were the target of the explosions given they were answering a report of a suspicious vehicle when it blew up.

Buck McCoy, who lives near the area, posted videos on Facebook that show water pouring down the ceiling of his home. Alarms blare in the background and cries of people in great distress ring in the background. A fire is visible in the street outside.

McCoy said the windows of his home were entirely blown out. “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 said.

“It felt like a bomb. It was that big,” he told the Associated Press. “There were about four cars on fire. I don’t know if it was so hot they just caught on fire, and the trees were all blown apart,” McCoy added.