As Australia reels from the Sydney siege and its unhappy end, many will be wondering what can be done for the hostages stuck for hours with the gunman in the Lindt cafe.

Amid the sea of flowers and mourners at Sydney's Martin Place, siege survivor Harriette Denny set up her own tribute for her slain boss, Tori Johnson.

The "fake sheik" behind the deadly Sydney cafe siege railed against Australian "terrorism" on his website a day before he took 17 people hostage.

PM John Key said the Sydney siege gunman highlighted the conundrum for authorities over protecting citizens against potential terrorism and over-stepping their powers.

Man Haron Monis brought a nation to its knees. After taking 17 people hostage he was in charge, helping empty the heart of Sydney.

Prime Minister Tony Abbott will urgently review how a lone gunman known to federal police and ASIO was able to take hostages in a Sydney cafe.

Government MP Mark Mitchell argues that the Sydney hostage drama is 100 per cent justification for the anti-terrorist legislation he helped bulldoze through Parliament last week.

Monis' former partner Noleen Hayson Pal, 30, was stabbed 18 times and set alight outside her Werrington unit in April 2013.

Whenever there is a dramatic event, social media instantly comes alive with comment and conjecture as facts vie for attention with fiction.

Just hours after the Sydney siege ended with the death of two hostages, crowds gathered to pay their respects.

Pop stars, comedians and Kevin Rudd's daughter are among critics of Rupert Murdoch for his insensitive tweet about the Sydney hostage crisis.

Hostages caught in Sydney's siege have revealed how some of them managed to escape when the gunman's back was turned.

Haron Monis was known to authorities for a string of offences.

Some hostages held in the Sydney cafe may have had thoughts of attacking the hostage takers as survival instincts "come to the fore", a psychologist says.

The MP who chaired the anti-terrorist legislation rushed through Parliament last week, MarkMitchell, says the bill was "100 per cent" justified.

The country’s highest Islamic office holder has condemned the actions of a gunman responsible for a hostage situation in Sydney’s CBD.

Father-of-four Craig Stoker had just bought a coffee at the Lindt Chocolat Cafe in Sydney's Martin Place when he walked out and bumped into a "crazy-eyed" man.

A New Zealander who saw the Sydney siege unfold has described seeing people cowering on their knees only moments after a gunman took them hostage.

Aucklanders can be confident the measures Sydney has in place to deal with hostage or terrorism emergencies would be available here - but on a smaller scale, a senior police source says.

A flurry of loud bangs erupted just after 4am NZ time as a swarm of heavily armed police stormed a downtown Sydney cafe where a gunman had taken hostages.

As the Sydney siege threatens to open up old prejudices, hashtag #illridewithyou has led a call for unity.

Here's what we know now about the situation in Sydney where a gunman has seized hostages.

The hostage drama in central Sydney has shut down the city's CBD. Click here for live updates from AAP.

New Zealanders caught up in the area where a hostage drama is unfolding in central Sydney - some who are still in lock down - have spoken about their experiences.

Martin Place in Sydney CBD is in lockdown after gunmen took hostages at the popular Lindt cafe this morning.

Bruno was turning up for his shift as a barista and waiter when he was ushered away at the door by police.