Breaking: Sydney On Lockdown as Dramatic Siege Unfolds #sydneysiege

The heart of Sydney, Australia, is currently in lockdown, as a siege unfolds at a downtown cafe. Reporting is still fuzzy and ongoing, but here's what we know so far: Police are responding to a situation at the Lindt Cafe in Martin Place, a central plaza in the city surrounded by banks and law firms, and not far from the state parliament buildings and the Sydney Opera House.

The number of hostages taken have not been confirmed. Channel Seven, a TV station with studios and offices in Martin Place, is reporting police sources as saying there are 13 people being held. The number of hostage-takers has also not been confirmed.

Twitter users have posted images of people, apparently hostages, with their hands against the windows of the cafe and holding up a black flag with Arabic writing on it. Guardian Australia is reporting the flag reads, "There is no god but the God, Muhammad is the messenger of God." It is not the Islamic State flag. Large parts of the area have been cordoned off.