Sydney siege: key points

FACTBOX: SYDNEY SIEGE KEY POINTS

* Up to 30 hostages held inside a cafe in Sydney's Martin Place.

* Black Islamic flag pressed up against shop window inside the Lindt Chocolate Cafe.

* NSW Police Commissioner Andrew Scipione says police have moved to a "footing" similar to dealing with a terrorist attack.

* Around six hours into the siege, three male hostages fled from the cafe. An hour later two female employees also emerged.

* The gunman, who calls himself "the brother", had reportedly demanded a flag of terrorist organisation Islamic State be delivered to the cafe and he wants to speak with Prime Minister Tony Abbott.

* Heavily armed police lock down CBD with Martin Place, Sydney Opera House, State Library and court houses evacuated.

* Siege chaos causes major traffic disruptions: Martin Place train station shut down and flights diverted in airspace above Sydney CBD.

* National Security Committee of Cabinet convenes, Prime Minister Tony Abbott describes the incident as "deeply concerning" and offers NSW all possible assistance.