Sri Lankan President Mahinda Rajapaksa says he was “deeply disturbed” by the hostage situation which continues to unfold in downtown Sydney on Monday morning, after a gunman entered a cafe and allegedly held its occupants.

Part of Australia’s largest city was on lockdown Monday after an armed gunman took several people hostage and forced two people to hold what appeared to be a black flag bearing Islamic slogans written in Arabic in the store’s window.

“Deeply disturbed about the hostage situation in Sydney. Sri Lanka stands united with Australia in fighting terrorism,” Rajapaksa said, in a Twitter message to Australian Prime Minister Tony Abbott.

Four hours after the incident began at the Lindt Chocolat Cafe in Sydney, New South Wales Police Commissioner Andrew Scipione said police had not made direct contact with the gunman, did not know his motivation and were not sure how many people were being held inside.

“We have not yet confirmed it is a terrorism-related event -- we’re dealing with a hostage situation with an armed offender and we are dealing with it accordingly,” Scipione said. However, Scipione did say that police were operating “on a footing consistent with a terrorist act.”

Estimates of the number of people held in the cafe have varied wildly. Chris Kenny, an associate editor and columnist for The Australian newspaper, left the cafe moments before the gunman entered. He estimated that there were approximately a dozen customers when he was inside, and between three and four staff.

However, Lindt Australia CEO Steve Loane has said that there are between 40 and 50 customers and employees inside the store.

Police were first called to the scene at approximately 9:45 a.m. local time Monday (5:45 p.m. ET Sunday). The cafe is located in Martin Place, a plaza in the heart of the city’s financial and shopping district that is packed with holiday shoppers this time of year.

Hundreds of police flooded into the area, streets were closed and offices evacuated. The public was told to stay away from the area, which is home to the state premier’s office, the Reserve Bank of Australia, and the headquarters of two of the nation’s largest banks. The state parliament house is a few blocks away, and the Sydney headquarters of the Seven television network is also nearby.