Roads will be closed between the Sydney CBD and Surry Hills today as school students march for more action on climate change.

The School Strike for Climate protests across the country are expected to attract thousands of attendees.

Motorists and commuters are advised to allow plenty of extra travel time, and follow diversions as instructed by NSW Police.

Bus services and light rail services will be affected.

From around 10:30am, roads between Camperdown and the CBD will close then progressively reopen as a march travels along City Road, Broadway, George Street, Liverpool Street, Kent Street and Bathurst Street to Town Hall.

Roads around Town Hall will start closing from 11:30am, ahead of the main march starting at around 12:45pm.

Roads between Hyde Park and Surry Hills will close from 12:30pm, including sections of Elizabeth Street, Park Street and Chalmers Street.

All roads are expected to reopen by 3pm.

Image: Jenny Evans/Getty Images