Spanish police says that a 57-story office tower in Madrid's business district has been evacuated due to an unspecified security threat.

Staff at the Torrespacio skyscraper received a phone call with the threat, a spokeswoman with the National Police said, prompting the tower's own security personnel to evacuate the building.

The spokeswoman, who wasn't authorized to be identified by name in media reports, said she couldn't provide specifics about the nature of the threat.

She said the tower had been evacuated by the time police arrived at the scene.

At 235 meters (770 feet), Torrespacio is one of four skyscrapers dotting the northern part of the Spanish capital's skyline.