"I ran down to the entrance of our work and pretty much screamed my head off that the place was being held up. About a minute, two minutes later the place was stormed with police everywhere ... they were coming from every corner of the street.
"I just thought it was a robbery, I didn't think that it was an Isis crisis - that was the last thing on my mind."
Mr Stirk said specialist armed police entered the Burger Bro before asking them to evacuate.
"I was just talking to the other chef I work with about Isis on Sunday and then that happened today, and I just can't believe how close to home [it's come]," he said. "It could have been our building, it's only metres [from] our entrance ... it's a bit too much to deal with."
Mr Stirk described seeing an employee from the Lindt cafe arrive for work after the siege began.
Watch: Australian PM Speaks on Sydney Cafe Siege
"He was knocking on the door ... and he looked through and saw his manager [being held hostage]."
Fellow Burger Bro employee Christina Tupou said she was in the restaurant's office, preparing the store for opening, when she heard the siege begin. "All I heard was screaming and people running in and out ... it was very frightening, and very unexpected."
Ms Tupou said they left the restaurant open as it was being evacuated to allow police to use it to "try and get a way in".
Christchurch-born Christy Johns, who works as a news producer at Channel 7, described the siege as terrifying. The network's newsroom is opposite the Lindt cafe.
"It's obvious that they wanted the media attention, because our Channel 7 offices in Martin Place just have one large glass window, and the Lindt cafe is directly opposite it," she said.
"We could see straight over there, and see all the workers with their hands pressed up to the glass.
"We thought it was a hold-up at first, and then as soon as the flag went up our hearts just sank, and we realised that it could be really something else with the hostage situation.
"They were just standing with their hands up on the glass, not moving. The guy inside got one of them to put up the flag," Ms Johns said.
The situation was "insane" and everyone was a bit shaken. "Hopefully it'll all end well - if it doesn't it'll hit hard, I think, being there and seeing it all unfold from the start."
New Zealanders Kate Alexander and Karna Luke had just walked past the Lindt cafe on their way to an 11am meeting when they remarked on how quiet it was for a Monday morning.
But when they got to their meeting place, the doors were locked and security staff had to let them in. It was only then they were told of the armed siege just metres away.
Aucklander Matthew Dale, 21, who works in a restaurant on Bligh St near Martin Place, was walking to start his shift when he came across a police cordon. He said the atmosphere was tense and people were talking about reports of an explosive device inside the building.
Watch: Hostages seen fleeing Sydney Cafe
A New Zealand-based cabin crew member for Virgin Australia, Arden Macdonald, was staying at a hotel close to the scene while on layover.
Speaking from within the cordon, he said the central city was eerily quiet.
"Everyone's silent, if they're talking to each other they're whispering. You could hear a pin drop."
Kate Hulbert, formerly of Napier, said her building was put in lockdown and everyone was "pretty scared".
Her building was a couple of streets away from the Lindt cafe, but armed police had confined tenants to their offices after reports the gunmen had explosive devices, she said.
"There is no one on the streets, it's just a complete ghost town.
"Everyone is just too scared to go outside."
Watch: Sydney CBD shutdown by siege
Hostage banner Islamic but not Isis'
The flag displayed by hostages held inside a Sydney cafe by an armed terrorist bears the words "There is no god but Allah, Muhammad is the Messenger of Allah" written in white Arabic on a black background.
Called the Shahada flag, it differs from the black-and-white flag used by the group Isis (Islamic State), which has carried out beheadings in Syria.
The flag belongs to the extremist group Jabhat al-Nusra, which is fighting the Assad Government in Syria.
Also known as the Al-Nusra Front or Victory Front, Jabhat al-Nusra is a Syrian-based Sunni extremist group that adheres to the global jihadist ideology of al-Qaeda, the group behind the 9/11 attacks in 2001.
According to Australian National Security guidelines issued by the federal Government, al-Qaeda in Iraq (AQI) sent operatives to Syria in late 2011 for the purpose of establishing Jabhat al-Nusra to fight the regime of President Bashar al-Assad.
The group publicly announced its presence in Syria in a January 2012 video statement.
Watch: Hostage Situation Erupts in Sydney
In early April 2013, Jabhat al-Nusra pledged allegiance to al-Qaeda leader Ayman al-Zawahiri and confirmed the group had received funding and operatives from AQI.
Jabhat al-Nusra's stated objectives are to remove the Assad regime and once that is achieved, to replace it with a Sunni Islamic state.
Although the group is affiliated with al-Qaeda, Jabhat al-Nusra has previously not emphasised an attack on Western targets or global jihad, focusing instead on the "near enemy" of the Syrian state. The Australian Government says that the group has received direct endorsement from online extremist forums aligned with al-Qaeda.
- Daily Mail, additional reporting Hawkes Bay Today
