Sydney to mark first anniversary of cafe siege

Australia's Sydney city on Tuesday marked the first anniversary of a cafe siege which left three people, including the gunman, dead.

Iranian self-styled Muslim cleric Man Haron Monis held 18 hostages inside the Lindt chocolate cafe on December 15, 2014.

The families of victims barrister Katrina Dawson and cafe manager Tori Johnson have gathered to join thousands of people at a twilight vigil outside the cafe, ABC reported.

The Dawson family said they were overwhelmed with support from around the world this past year.

"Whilst nothing can replace the void that Katrina's death has brought to our lives, the warmth of those many voices of support has helped us enormously on our darkest days," the family said in a statement.

Photos showing Dawson and Johnson sit amongst the floral tributes left outside the cafe in the city's Martin Place.

Five nights of light projections onto the Lindt Cafe building will follow after this Tuesday's memorial.

Prime Minister Malcolm Turnbull said the whole city woke in shock and grieved together, responding in solidarity.

"A whole nation resolved to answer hatred with love," Turnbull told the gathering.