Sydney, the Hunter and the Illawarra will again face very high fire dangers on Wednesday as the mercury nudges 30 degrees and humidity levels dive.

The Harbour City is forecast to reach 28 degrees, as is much of the city, according to the Bureau of Meteorology.

The NSW Rural Fire Service said fire risks would be elevated by humidity levels dropping to as low as 13 per cent with north-westerly winds gusting to 55 km/h.

Smoke over Sydney's northern beaches from hazard reduction burns in the Ku-ring-gai Chase National Park may return on Wednesday morning. Credit:Nick Moir

Sydney residents may again smell smoke on Wednesday morning from hazard-reduction burning in the Ku-ring-gai Chase National Park.