A major downtown intersection was closed Monday morning and will not reopen until at least Tuesday at noon due to an unstable antenna on the roof of Trump Tower.

Police have closed part of Bay Street near the 65-storey tower as well as parts of Richmond and Adelaide streets since Monday morning's rush hour for safety reasons. The closure lasted throughout the entire morning rush hour, and police say it will include the evening rush hour as well as Tuesday morning's rush hour.

Police have taken to calling the incident #TrumpUnstableAntenna on social media.

A building employee first spotted the moving antenna and alerted police. Toronto Police Sgt. Kevin Hamilton said since arriving on scene, he has seen the antenna sway.

"It was a little disturbing," Hamilton said, adding some people have seen the structure move by as much as a metre.

The street in front of Trump Tower, seen here, was blocked off Monday morning. (Tyna Poulin/CBC)

The city asked the owners of Trump Tower "to ensure the building does not pose a risk to the public," but has not yet received a reply.

Mayor John Tory said in a statement he is "very concerned about the impact on traffic in the downtown core." He wants an investigation and said he is "determined that responsible parties are held accountable."

A strip of LED lights called Lightline, designed by artist Michael Snow, runs up the edge of the building to the top of the tower where the antenna is located. It's unclear if the installation is affected.

Pedestrians are being kept away from the intersection.

Engineers are now on scene examining the antenna mast.