Police Chief John Drake said the announcement warned the "bomb would explode in 15 minutes.""} 64:{"position":5,"content":"

About the same time, police received an emergency call of "shots fired" in the downtown tourist area, said Nashville police spokesman Don Aaron. After arriving, they called in the bomb squad, which was on its way when the explosion occurred.

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

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Fire officials said three people suffered minor injuries.

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Moments before the blast, police officers went door-to-door in nearby buildings to hustle residents to safety and motioned a man walking his dog near the vehicle to change direction.

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"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."

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Andrew McCabe, a former deputy FBI director, told CNN an explosion of this size would be investigated as a possible act of terrorism, whether domestic or international.

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Police said it was unclear if anyone was inside the vehicle and the motive was unclear. McCabe said police may have been the target of the explosions given they were called to the scene before the blast.

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Most of the buildings on the tree-lined street with shops and offices were closed given the hour and Christmas holiday.

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The explosion, which could be heard for miles and felt nine blocks away, knocked one off

Warning plays from RV before it explodes in Nashville in 'intentional act'

A motive for the explosion was not disclosed by police.

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