New York, Dec 7: CNN's offices and studios here were evacuated on Thursday night because of a phoned-in bomb threat. But police and the network have issued an all-clear message saying it was safe.

"The NYPD (New York Police Department) 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 on Friday.

"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 NYPD tweeted.

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

Several fire alarm bells rang inside the newsroom, signaling an evacuation shortly after the call was received.

Staffers evacuated the offices in the Time Warner Centre building.

The network temporarily went to taped programming for about half hour before going live from the street while police investigated.

The network's bureau was evacuated in October after a package with an explosive device, addressed to former CIA Director John Brennan, was discovered, officials said.

That package was among more than a dozen improvised explosive devices sent to prominent Democratic politicians and donors around the country in October. None of the devices detonated, and no one was injured.

Suspect Cesar Sayoc, 56, was charged with five federal crimes and is currently in custody waiting for trail. If convicted, he could receive up to 48 years in prison.

CNN's New York offices evacuated after 'bomb threat'