We do believe that the explosion was an intentional act.

Fire officials reported taking three people to the hospital, but none were critically injured.

Police reported seeing the vehicle when they responded to an emergency call of shots fired in the downtown tourist area early in the morning, without specifying what made it suspicious, Police said Circumstances about the motorhome prompted officers to call the bomb squad.

The bomb squad was on the way when the explosion occurred, Andrew McCabe, a former deputy F FBI director, told CNN.

An explosion of this size would be investigated as a possible act of terrorism, whether domestic or foreign.

Moments before the blast, police officers went door to door in nearby buildings to hustle residents to safety, police said.

It was not immediately clear if anyone was inside the motor home when it exploded.

Most of the buildings were closed, given the hour and Christmas holiday in the heart of the city.