Emergency services were called at around 7.30am on Thursday, June 25, to reports that a man had barricaded himself inside a property in Osbourne Close, in Hemlington.
Cleveland Police has said the man has reportedly made threats.
A cordon is in place and around 20 homes have been evacuated.
Armed officers and the bomb squad are in attendance at the incident as well as firefighters and paramedics.
Residents and emergency services have been given food and water and there is also a police federation welfare van at the scene.
A large police cordon is in place