The archbishop of Sydney has called for prayers after several people were taken hostage in the Australian city, reminding citizens to not turn on one another or "undermine our sense of security."

"My thoughts and prayers - and those of the entire Catholic community - are for the hostages and their families, and for our police officers who are working to resolve this situation peacefully," said Archbishop Anthony Fisher in a Sydney Archdiocese press release.

The stand-off between police and a gunman concluded in the early hours of the morning of Dec. 16. Several gunshots were fired shortly before the crisis ended, and medical personnel were at the scene to aid the wounded.

An estimated 30 clients and 10 staff workers of a Lindt Cafe in Sydney's Martin Place district were taken hostage at around 9:45 in the morning of Dec. 15, according to local reports.

Three hostages were seen fleeing the cafe nearly six hours after the siege began, followed by two others shortly afterward.

Some hostages have been seen holding up a black flag with white Arabic writing in a window of the cafe' similar to that used by some jihadist groups, local media reported. However, it is different from the flag used by Islamic State militants.

The gunman has been identified as Man Haron Monis, Iranian-born cleric who had been granted political asylum in Australia.

Hundreds of armed police have cordoned off the area, a heavily-trafficked pedestrian thoroughfare close to several important government buildings, including Parliament House and the United States Embassy.

"Australia is a peaceful, open and generous society - nothing should ever change that," said Prime Minister Tony Abbott, who then urged Australians "to go about their business as usual."  

Speaking later in the day, after chairing a meeting of the national security committee in Canberra, Abbot said it was "profoundly shocking" that the hostages were being held "by an armed person claiming political motivation."

In the afternoon, Premier of New South Wales Mike Baird said: "We are being tested today in Sydney. The police is being tested, the public is being tested, but whatever the test we will remain a democratic, civil society.

"There could be some disruption obviously, we are asking also to be patient - we will get through this."

Monday's siege comes after an anti-terrorism raid in September in which a man was charged with plotting to a beheading in Martin Place.

The Australian parliament approved new anti-terrorism laws in October, including a provision to stop Australian citizens from fighting in overseas conflicts.

"Two of the greatest attributes of our nation are its atmosphere of ease and safety and its history of harmony between people of different ethnic, religious and political affiliations," said Archbishop Fisher. "Today's incident will test our determination to remain such a society. We must not allow it to turn us on each other or to undermine our sense of security."

"At Christmas we look forward to the birth of Jesus as Prince of Peace. Let us pray to him, recalling God's promise to Jeremiah: 'So call upon me and I will answer you, and lead the hostages to safety'."