Three people have come running out of the Sydney cafe where a siege has been underway for nearly six hours.

Three men managed to leave the Lindt Cafe in Martin Place. One was wearing a brown company apron.

The three are understood to have escaped, rather than being released by the hostage taker, who took control of the cafe this morning and is believed to be armed. A black flag with an expression of faith in Islam was seen in the window of the cafe.

There are less than 30 people in the cafe, including 10 staff, but police were unable to confirm the number.

Armed police have surrounded the building and cleared an area of several blocks in all directions around Martin Place, which includes the headquarters of the Commonwealth Bank and the Reserve Bank of Australia.

Police negotiators have had contact with the gunman and deputy police commissioner Catherine Burn said the motivations of the gunman are not known.

Nobody has been harmed at this point.

“It might take a bit of time and I can assure you we want to resolve this peacefully,” Burn said.

“Our number one priority is the safety of everyone concerned.”

Burn asked people in buildings facing Martin Place to stay in their offices and police will advise when they can leave.

A police hotline has opened for general information about the incident, including information about other government services. Call 1800 227 228.

Police said do not call 000 or the Police Assistance Line.

There is also a “safety site” in Hyde Park.

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