A man watching from the 15th floor of the Aon building, Tor Bayer, says a swarm of officers with guns have set up multiple cordons around the Commercial Bay Precinct.
The Eagle helicopter is circling overhead and ambulances are also there.
More police vehicles have been seen heading towards the area.
Police say the situation is currently contained to a building in lower Queen Street, which is under construction.
Bayer spoke to Corin Dann.
