Nashville police were able to usher people to safety before an explosion rocked downtown Nashville on Christmas morning in what authorities are calling a deliberate act, while a warning message was broadcast urging people to evacuate moments before the blast.

Officers with the Metro Nashville Police Department carried out door-to-door and apartment-to-apartment checks and managed to get people to safety shortly before the blast, according to statements made at a press conference.

There was a loudspeaker warning people to clear the area before the massive blast, according to a Metro Nashville Police spokesperson and surveillance footage.

“All buildings in this area must be evacuated now,” a voice could be heard in the video. “If you can hear this message, evacuate now,” the warning continued, before the blast occurred.

The explosion shattered windows, damaged buildings, and wounded three civilians.

One officer was knocked down to the ground by the explosion, while another had temporary hearing loss, police said at the presser. No officer sustained serious injuries in the incident, police said.

Police spokesman Don Aaron said three people were taken to area hospitals for treatment, although none were in critical condition. He added that the 6:30 a.m. blast was believed to be “an intentional act.”

Police earlier said they believe a vehicle was involved in the explosion and at the presser said they are unsure whether there was anyone inside the vehicle, said to be an RV.

Metro police said in a statement that canine teams are doing protective sweeps in the downtown area and that traffic downtown is restricted.

The FBI will be taking the lead in the investigation, according to spokesman Joel Siskovic. Federal investigators from the Bureau of Alcohol, Tobacco, Firearms, and Explosives were also on the scene. The FBI is the primary law enforcement agency responsible for investigating federal crimes, such as explosives violations and acts of terrorism.

Officers were responding to a shots fired call in downtown Nashville when they spotted a suspicious RV and called the bomb squad, according to a press release.

While the bomb squad was heading to the scene, the RV exploded, the press release said.