A man is believed to be in police custody after reportedly arming himself with a knife and running through the Sydney CBD.

NSW Police spokespeople confirmed a man was taken into police custody at around 2pm this afternoon on Clarence Street near Wynyard Station.

There are no concrete reports regarding injuries at this stage though unconfirmed reports suggest multiple people may have been hurt.

Police have blocked off the area around the incident and are urging people to stay away from the area.

Emergency personnel are currently on the scene.

More on this story as it develops.

Image: Twitter / Laura Jayes