At least five hostages, including two women, have fled the Lindt Chocolate Café in Sydney’s Martin Place, Australia, which was hijacked by an armed gunman.

The gunman entered the café with a bag just before 10am local time, taking an undisclosed number of staff and customers hostage and forcing few of them to hold up a black flag with white Arabic writing against the café’s windows.

The circumstances of hostages’ exit from the building, which is located in the central business district of Sydney and is heavily surrounded by police, currently remain unclear.

"At this stage, those motivations are not known and it would not be good to speculate."

Lindt Australia chief executive officer was quoted by as saying that nearly 40 to 50 people, including customers and staff, are inside the café.

However, the New South Wales Police has put the number as fewer than 30 and noted that the situation was not being treated as a terror incident.

New South Wales Police deputy commissioner Catherine Burn said the police negotiators had made contact with the gunman but are yet to understand the motive behind the siege.

"At this stage, those motivations are not known and it would not be good to speculate," Burn said.

"It might take a bit of time but we want to resolve this peacefully."

Australian Prime Minister Tony Abbott said: "This is obviously a deeply concerning incident but all Australians should be reassured that our law enforcement and security agencies are well-trained and equipped and are responding in a thorough and professional manner.

"We don’t yet know the motivation of the perpetrator. We don’t know whether this is politically motivated, although obviously there are some indications that it could be."

Abott has also convened a National Security Committee of Cabinet meeting in Canberra for briefings on the situation that that has shut down central Sydney.

Australia has recently raised its threat level to high and remains on high alert for attacks by radicalised Muslims or by home-grown militants returning fighting with the Islamic State in the Middle East.

Defence Technology