At the centre of a new memorial in Sydney's Martin Place sits a bunch of hydrangeas and another of sunflowers – the favourite flowers of Lindt Café siege victims Katrina Dawson and Tori Johnson.

Ms Dawson, a barrister, and Mr Johnson, the Lindt Café manager, were killed in the 17-hour siege, carried out by Man Haron Monis on December 15-16, 2014.

On the third anniversary of the hostage tragedy, more than 200 flowers in mirrored cubes have been inlaid into the pavement just metres from where it unfolded, as a permanent memorial to honour the victims.

Bouquets of hydrangeas and sunflowers are placed on the memorial - the favourite blooms of the victims. (AAP)

Each mirrored cube contains a handcrafted flower. (AAP)

"No Australian will ever forget the heartbreaking events that unfolded at Martin Place three years ago, but none more so than the loved ones of Tori and Katrina – two young, wonderful Australians killed by an act of evil and terror," New South Wales Premier Gladys Berejiklian said today.

Ms Berejiklian unveiled the enduring memorial inspired by the thousands of bouquets that were left as tributes in the days after the siege, in the presence of the Johnson and Dawson families.

"We gather to dedicate a permanent memorial to the victims to ensure that Australians today, and for generations to come, will always understand and reflect what took place," she said.

Ms Dawson's daughter Chloe and niece Samantha Dawson presented the hydrangeas to her husband Paul Smith, while local school student Jack Tighe presented the bouquet of sunflowers to Mr Johnson's partner Thomas Zinn.

Local school student Jack Tighe hugged Mr Johnson's partner, Thomas Zinn, after presenting the bouquet of sunflowers. (AAP)

Katrina Dawsons's daughter Chloe hugs her father Paul Smith during the unveiling. (AAP)

The families, including the victims' parents, then stepped up to view the floral tribute before they were joined by many of the survivors and their supporters.

Sydney siege victims Katrina Dawson and Tori Johnson. (Supplied)

Martin Place was flooded in a sea of colour as people shared in their grief for the victims and hostages of the Lindt cafe siege. (AAP)

In the wake of the siege, florists sold out of flowers as Sydney workers, residents and families flocked to the site to pay their respects and show their solidarity.

The memorial was designed by Professor Richard Johnson and artist Jess Dare.

Each cube contains an individual handcrafted flower, which will reflect the sun during the day and be illuminated from above at night.

"This memorial draws strength from its beauty and simplicity," Ms Berejiklian said.

"It says more that we could do with words alone. It will indeed be a place to reflect."

Dignitaries, family and close friends inspect the memorial honouring Katrina Dawson and Tori Johnson. (AAP)

Earlier today, the New South Wales governor, on behalf of the Governor-General, announced that Mr Johnson will be recognised with a Star of Courage and Katrina Dawson with a Bravery Medal, under the Australian Bravery Decorations awards for displaying acts of courage.

The awards will be formally recognised "at a later date".

"We will always celebrate the full, generous, loving lives that they lived. We will always honour the incredible bravery and selflessness they showed to the very end," Ms Berejiklian said, also acknowledging the 16 other men and women who were held hostage in the siege.