Watch the moment police storm Lindt cafe in Sydney

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(CNN) — Police in Sydney, Australia have stormed a cafe where hostages have been held for more than 16 hours.

More than 16 hostages have been seen running from the building.

The fate of the gunman, who has been identified as Man Haron Monis, is not known.

Also known as Sheikh Haron, he pleaded guilty in 2013 to writing letters to Australian service members saying they were “Hitler’s soldiers,” according to Australian media reports.

He is probably acting alone and does not appear to be part of a broader plot, additional U.S. law enforcement and intelligence sources say.

Beyond the demands for the flag and phone call, precisely what he wants remained murky late Monday.

Hundreds of police officers, including snipers, surrounded the Lindt Chocolate Cafe in Sydney’s central business district shortly after the gunman took over the building at 10 a.m. Monday (6 p.m. ET on Sunday).

Chilling images from Australian media on Monday showed people, believed to be hostages, with their hands pressed against the cafe’s windows. They were holding up a black flag with Arabic writing on it reading, “There is no God but God and Mohammed is the prophet of God.”

Five hostages sprinted out of the cafe toward heavily armed police officers several hours into the standoff, sending the gunman into an agitated tirade, according to an Australian reporter.

Chris Reason, a correspondent for CNN affiliate Seven Network, said the gunman became “extremely agitated” when he realized what had happened and “started screaming orders” at the remaining hostages.

Reason said he could see the gunman pacing past the cafe’s windows from his vantage point at the network’s nearby offices. He described the man as unshaven, wearing a white shirt and black cap and carrying a shotgun.

The gunman made his demands for a flag and phone call through hostages who contacted several media organizations, CNN affiliate Sky News Australia reported.

Some had also reportedly posted messages to social networking sites and the YouTube online video service. Police urged media early Tuesday not to show the videos.

As night fell, Reason said the cafe’s lights had been turned off, plunging the interior into “complete darkness.”

The incident left Australians shaken.

“We are doing all we can to set you free,” New South Wales Police Commissioner Andrew Scipione said at a news conference Monday, directing his comments to the hostages and their loved ones.

Abbott called the incident “profoundly shocking.”