2014 Sydney hostage crisis
After the siege began, a staged exclusion zone was established with thousands of people evacuated from nearby buildings, including from the floors above the café. The Sydney Opera House was evacuated after a suspicious package was found; however, reports were unconfirmed by police. The US Consulate General in Sydney, located in Martin Place, was also evacuated. Some Sydney schools were put in "white level lockout" due to the hostage situation, which meant that no school group was permitted to leave the school grounds.
Siege
A siege occurs when an attacker encounters a city or fortress that cannot be easily taken by a quick assault, and which refuses to surrender. Sieges involve surrounding the target to block the provision of supplies and the reinforcement or escape of troops (a tactic known as "investment"). This is typically coupled with attempts to reduce the fortifications by means of siege engines, artillery bombardment, mining (also known as sapping), or the use of deception or treachery to bypass defenses.