While an unidentified gunman continues to hold an unknown number of hostages inside the Lindt Chocolat Café in Sydney's central financial district, Australian police are preparing to negotiate with the hostage taker through the night. Authorities have also sealed off the surrounding areas and evacuated people from nearby buildings.

At a press briefing Monday, New South Wales Police Commissioner Andrew Scipione said there is no evidence that anyone inside the café had been injured in the siege so far, and added that police activity was currently centered on the café. With the hostage taker believed to be an Iranian Muslim, the official also warned against any reprisal attacks on Muslims or other minority communities in the country as a result of the incident, which began around 9:44 a.m. local time (5:44 p.m. EST, Sunday).

Authorities have referred to a single gunman, but it is not clear if there are more inside the café. The hostages were reportedly made to hold an Islamic flag in the window, triggering concerns of a terrorist attack. Later, according to reports, he made two demands -- one, to be provided with a flag of the Islamic State group, and two, to speak with Australian Prime Minister Tony Abbott.

On Monday, mosques, synagogues and churches across Australia called on people to gather and pray for the safety of the hostages inside the café. Meanwhile, several Muslim groups in the country condemned the incident, urging all Australians “to stand together.”

“We reject any attempt to take the innocent life of any human being, or to install fear and terror into their hearts,” according to a joint statement signed by over 40 Australian Muslim groups. “We remind everyone that the Arabic inscription on the black flag is not representative of a political statement, but reaffirms a testimony of faith that has been misappropriated by misguided individuals that represent no one but themselves.” 

According to reports, the Arabic script on the flag held aloft inside the cafe reads: “There is no God but Allah, and Muhammad is his messenger,” which is a basic tenet of Islam.

Scipione also said at the briefing that other buildings in the city, including the Sydney Opera House, had been checked and cleared. ABC News in Australia had reported that the suspect is known to NSW Police. However, when asked about the identity of the gunman, Scipione declined to provide any details.

“We won’t go into the details about who is in there, how many are in there. We are not in a position to do that at the moment,” Scipione said. “At this stage in terms of numbers, who they might be, we are not at liberty to go into that information… I understand no-one has been injured. And we are grateful.”

About six hours into the standoff, three people managed to exit the café, and about an hour later, two women left the cafe, bringing down the total number of hostages by five. However, police did not confirm if the five had escaped or were released by the suspect. It was also unclear how many people remained hostage inside the cafe.

“We don’t yet know the motivation of the perpetrator,” Abbott said in Canberra. “We don’t know whether this is politically motivated, though obviously there are some indications that it could be.”