STORY HIGHLIGHTS
- Authorities have not yet had direct contact with the hostage taker
- Australia's PM says it's unclear whether the violence is politically motivated
- Local media carry images of people holding a black flag with Arabic writing
- A CNN affiliate reports that at least 13 hostages are being held in a cafe
Sydney (CNN) -- [Breaking news update at 12:19 a.m. ET]
Police negotiators have had contact with a hostage taker in the cafe where an unspecified number of people have been held for hours, said New South Wales Police Deputy Commissioner Catherine Burn.
[Breaking news update at 12:05 a.m. ET]
Three people ran out of a Sydney cafe where an unidentified person or people had taken hostages Monday, CNN affiliate Seven Network reported.
[Original story posted at 11:55 p.m. ET]
Hundreds of police officers on Monday shut down a usually bustling area in the heart of Sydney, where an unconfirmed number of people are being held hostage in a popular cafe.
Chilling images from local media showed people, believed to be hostages, with their hands pressed against the glass of the Lindt Chocolate Cafe in Sydney's central business district.
Footage showed them holding up a black flag with Arabic writing on it that reads: "There is no God but God and Mohammed is the prophet of God."
Authorities said many of the details about the situation remained unclear, including the number of people inside the cafe and the motivations of the hostage taker.
"We don't know whether this is politically motivated, although obviously there are some indications that it could be," Australian Prime Minister Tony Abbott told reporters.
The Islamic writing on the banner stoked fears that the crisis in Sydney could be linked to extremists. Australia, which is part of the international coalition fighting the terrorist group ISIS in the Middle East, said in September that it had foiled a plot by Islamic militants to carry out a public execution.
New South Wales Police Commissioner Andrew Scipione said it wasn't yet clear whether the situation at the cafe was a terrorist event but that police are on "a footing that would be consistent with a terrorist alert."
He said police haven't so far had direct contact with the armed hostage taker, who appears to have taken staff and customers captive as people were heading to work on Monday morning in the Martin Place area.
Chris Kenny, an editor at The Australian newspaper, said he was at the cafe Monday morning. He left shortly before the siege started.
"As police quickly swarmed and cleared the area, I turned to see a man against the window, facing out with his hands raised," he wrote in his account of the incident. "At first I was relieved thinking this was the gunman responding to police -- but soon the awful realisation the customers were being forced against the windows."
CNN affiliate Seven Network reported that at least 13 people are being held at the cafe, but Scipione declined to say how many were in there.
Police barricaded off streets and evacuated buildings near the cafe, bringing an eerie quiet to a district typically buzzing with pedestrians and vehicles.
The Martin Place train station was shut down, according to police. They urged people to stay away from the area, but some local office workers gathered at the scene to try to find out what was going on.
The buildings evacuated included U.S. Consulate General, said Alicia Edwards, a spokeswoman. All personnel have been accounted for, although it's not known whether there are any U.S. citizens among the hostages. U.S. President Barack Obama has been briefed on the situation.
CNN's Anna Coren reported from Sydney; Dana Ford reported and wrote from Atlanta; and Jethro Mullen reported and wrote from Hong Kong. CNN's Hilary Whiteman, Chieu Luu, Shimon Prokupecz and Evan Perez contributed to this report.
