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

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.

There was Bali, but it was Westerners - not Australians, specifically - who were targeted.

The killing of hostages in Sydney has not deterred New Zealanders from flying to Australia.

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.

Against a backdrop of fear and uncertainty following the hostage taking in Sydney, thousands of ordinary Australians turned to social media to spread a message of unprecedented tolerance and solidarity.

These are the six words that say it all. "I'll be back at work tomorrow."

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

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.

Could it happen here? That is a question to haunt this country whatever the outcome of the hostage crisis in Sydney.

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.

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

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.

Read how the Sydney siege unfolded during the day.

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.

The cafe siege in Sydney was only to be expected after Islamic State urged followers to launch such “lone wolf” attacks, specifically mentioning Australia, terror experts say.

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

Parliament has just passed legislation aimed at stopping would-be foreign fighters from leaving New Zealand to join Islamic State in Iraq.

US embassies have been told to prepare for violent protests ahead of a report into the CIA's use of torture.

The father of a teenager from Cardiff is thought to be the first Briton to have rescued his son from the jihadist group Islamic State.

Thirty-five people were killed and 150 injured when multiple explosions tore through the central mosque in Kano, police said.

The Government is legislating at breakneck pace to pass a bill it calls "Countering Terrorist Fighters Legislation".