The centre was evacuated for the first time Wednesday after crude pipe bombs were sent to CNN, along with President Barack Obama, Hillary Clinton, CNN, Rep. Maxine Waters of California and others.

CNN is a frequent target of Trump, who routinely calls the news media the "enemy of the people" and belittles critical coverage as "fake news."

Photos of the suspicious package sent to CNN on Wednesday show what appears to be a pipe bomb wrapped in black electrical tape.