NSW govt working to retain siege tributes

The NSW government is speaking to authorities in London and Boston about the best way to retain the flowers at the ever-growing memorial for the victims of the Sydney siege.

Bouquets, condolences and other tributes have overtaken Martin Place since the siege ended on Tuesday.

The City of Sydney council is working with the government, a spokesman for Premier Mike Baird said.

"All flowers will be composted into a clean compost and laid at an appropriate memorial site," he said.