Sydney is in danger of becoming “a throwaway city of junk buildings” built on the cheap to be knocked down every 30 years, a leading architect and City of Sydney councillor has warned.

Philip Thalis also criticised the NSW government's sell-off of public buildings, which he said constituted "a theft of public assets", and the destruction of heritage buildings and streetscapes caused by projects such as the Sydney Metro, Westconnex and roadworks.

Philip Thalis said the sell off of public buildings such constituted "a theft of public assets". Credit:Peter Braig

"Public Sydney risks becoming privatised Sydney," said Cr Thalis, speaking at the National Trust Heritage Awards 2019 on Friday.

"We know that regardless of political persuasion, privatisation is deeply unpopular with the majority of citizens, and constitutes a theft of public assets that would otherwise have been available to future generations."