Parts of Sydney's CBD will be locked down to traffic on Friday as students take to the streets to protest against inaction on climate change.

Park Street will be closed between George and Elizabeth streets from 1pm, while parts of Elizabeth, Castlereagh, Pitt and Druitt streets will also be closed.

Thousands of students protested in Martin Place regarding climate change policy in November last year, and will gather again in Sydney on Friday. Credit:Nick Moir

"Traffic is expected to be heavier than usual on nearby roads including Market Street, King Street, College Street and Macquarie Street," the Transport Management Centre said.

The protest gathering will begin at noon at Sydney Town Hall before the march starts about 1.15pm, moving to Hyde Park.