Police were called to the incident on Oxford Tce, opposite the justice precinct, about 3.45pm after reports one person had been injured.
Armed police were seen surrounding St Michael and All Angels church.
St Michael and All Angels church on Oxford Tce.
A police spokeswoman said a 38-year-old man, who was thought to be carrying a weapon, had locked himself in a commercial premises on Oxford Tce before being detained.
The spokeswoman said the situation is being treated as a mental health incident.
St John spokesman Gerard Campbell said ambulance crews were stood down by police.
