(CNN) Police and CNN have issued an all-clear message after the network's New York offices and studios were evacuated Thursday night because of a phoned-in bomb threat.

"The NYPD has now given us the all clear, and employees have been permitted to return to the building,"CNN Worldwide president Jeff Zucker said in an internal memo to staff. "The building is secure and safe for everyone to return in the morning."

"We appreciate the swift action by the local authorities, and the patience and professionalism of all the employees who were impacted."

The threat was not substantiated, the New York Police Department tweeted.

The threat came Thursday night when a caller indicated there were five devices in the building, according to a law enforcement source.

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