Officials believe that a Christmas morning explosion in downtown Nashville that injured at least three people and damaged dozens of buildings was an intentional act.

In a brief news conference Friday morning, Metro Nashville Police spokesman Don Aaron said the department's hazardous devices unit was headed downtown in response to a call about a suspicious vehicle when there was a "significant" explosion linked to that vehicle around 6:30 a.m. CT."We do believe that the explosion was an intentional act," Aaron said.

Three people have been transported to hospitals from the scene, but none are in critical condition, according to Nashville Fire spokesman Joseph Pleasant.

The force of the explosion knocked down one officer, Aaron said, and caused hearing loss in another -- hopefully temporarily, he said. But no officers were significantly injured.

The incident is under investigation by multiple agencies, both local and federal, including the FBI and the ATF, Aaron said in an earlier news briefing.

Police and Tennessee Highway Patrol were conducting a shutdown of the area for the investigation.Acting US Attorney General Jeff Rosen was briefed on the incident early this morning, according to his spokesman, "and directed that all DOJ resources be made available to assist in the investigation."

The White House said that President Donald Trump has been briefed on the incident as well and would receive "regular updates." Tennessee Gov. Bill Lee said in a statement on Twitter that the state would "supply all the resources needed" to determine the cause of the explosion.

'Everything on the street was on fire'

Eyewitness Buck McCoy told CNN the explosion took place right in front of his home, causing his windows to be blown in."Everything on the street was on fire," he said.

"There were three cars that were fully engulfed." McCoy said he was originally woken up by what he believed were gunshots about 10 minutes prior to the explosion. He got up and looked out the window, he said, but went back to bed when he didn't see anything.

Asked if the noise he heard could have been something other than gunfire, McCoy emphasized that he believed it was, saying he owns a gun and goes shooting, so he's familiar with the sound of gunshots.

Investigators are doing a secondary search of buildings downtown, particularly those on 2nd Avenue, to make sure no one is in need of help, Aaron said.

Prior to the explosion, officers had gone door-to-door or apartment-to-apartment to inform residents of the situation. One man walking a dog on 2nd Avenue was redirected by an officer just before the RV exploded, he said.

Officials do not know whether anyone was inside the vehicle when the explosion occurred, he said. Police are not aware of any other attempted explosions.Nashville Mayor John Cooper told CNN that dozens of buildings have been damaged, mostly from having glass blown out.

Some buildings have been evacuated, the mayor said, but he did not know how many buildings or how many people had been impacted."Right now, there's just a whole lot of glass damage on 2nd Avenue," he said.

The street is on the edge of the Tennessee city's hospitality and tourist district in an old, historic part of town.

Cooper told CNN affiliate WSMV that the explosion was "clearly done when no one was going to be around."

"Fortunately not many people are here," he said.Footage from CNN affiliate WTVF showed smoke rising from a fire on the street, with debris littering the area. McCoy told CNN that when he looked outside after the explosion, trees had fallen and broken glass was everywhere.

He saw people filing out of their apartments with their animals. Firefighters told him to get as far away from the area as possible, he said. "There's just nothing left on 2nd Avenue," he said.