The gunman took an unknown number of people hostage at the height of Monday morning's rush hour and the siege is ongoing. Here are the facts we know:

:: At least one gunman stormed the Lindt cafe in Sydney at around 9:45am local time (10:45pm GMT).

:: Police were alerted when a woman reported seeing a man carrying a gun in a blue bag.

:: The man appears to be middle-aged, with a beard, and is wearing a black and white headband.

:: A flag with Arabic writing was displayed at the cafe window and several hostages were seen with their hands up against the window.

:: The writing on the flag appears to be the shahada, or profession of faith in Islam, and says: "There is no god but Allah; Mohammed is the Messenger of Allah."

:: The scene of the drama, Martin Place, is in Sydney's financial centre and houses several prominent buildings, including the New South Wales parliament, the US consulate, the country's central bank and the Commonwealth Bank of Australia.

:: Some six hours into the siege, three men emerged from the popular cafe and ran for their lives, two from the front door and one from an emergency exit.

:: Around an hour later two women who appeared to be staff members also fled into the arms of police.

:: It is understood that they all escaped and were not released.

:: Police have confirmed that negotiators have made contact with the gunman.

:: His motives are unknown. The two female hostages told Channel Ten news the gunman claims there are four bombs; two inside the Lindt cafe and two in Sydney's financial district.

:: It is not clear how many hostages are being held. Reports vary from eight to 50 people.

:: However, police said the numbers are "not as high as 30".

:: Police say they do not believe anyone has been harmed.

:: Australian PM Tony Abbott said there are indications the siege could be politically motivated.

:: Australia raised its terror threat level in September.

:: The Irish consulate in Sydney has closed and it is advising people to maintain a "high level of vigilance."