The streetcars were stopped as a result.
The Manchester Evening News is trying to contact Greater Manchester Police for comment.
Pictures and videos taken at the scene show a large police cordon in place.
It appears to start around the upper end of Piccadilly Gardens, closest to Portland Street, and extend all the way to Market Street.
It is understood that a rally had taken place in the gardens earlier Thursday evening.
Greater Manchester Police officers were at the scene.
Metrolink said due to a “police incident” no service was crossing Market Street to Manchester Piccadilly station.
Some lines were diverted via Exchange Square.
There are also no services in Shudehill and Market Street.