Australians have been laying flowers at the scene of a deadly hostage siege that ended with a police operation and the death of three people, including the hostage-taker, in Sydney.

Crowds have gathered at the site of the incident in Martin Place as social media have been flooded with expressions of fear and dismay and pictures of the city harbour and skyline.

Most of the hostages escaped but the cafe manager, 34, and a 38-year-old barrister and mother-of-three died in Monday’s operation while six more people were injured, including three women with bullet wounds.

The attack was staged by Iranian-born Man Haron Monis, who also died in the incident.

- 50 year old Iranian refugee who moved to Australia

– Was facing charges for being an accessory in the murder of his ex-wife

– Also faced more than 50 allegations of indecent and sexual assault

- Was convicted to 300 hours of community service for sending hate letters to families of dead Australian soldiers

Andrew Scipione, New South Wales (NSW) police commissioner, said there had been 17 hostages in total.

The hostage crisis had begun early on Monday and lasted around 16 hours.

Tony Abbott, Australia’s prime minister, called the siege a “brush with terrorism”.

“He had a long history of violent crime, infatuation with extremism and mental instability,” he said.

“As the siege unfolded … he sought to cloak his actions with the symbolism of the ISIL death cult.”

Flags on all government buildings were ordered to be flown at half-mast following the incident.