Three people have run out a fire exit of a Sydney building where a hostage situation has been unfolding.

It is not clear whether they were hostages or whether they were escaping from another area of the building where the hostage situation has been ongoing since Monday morning.

The two people were seen on live video footage bolting out of the door past heavily armed police and then disappearing around a corner.

The potential development came six hours after a gunman took an unknown number of people hostage inside a downtown Sydney chocolate shop and cafe at the height of Monday morning rush hour.

(AP)