An expected southerly change may spread bushfires burning across NSW, the state's rural fire service warns.
Firefighters are bracing for a night of strong winds and thunderstorms, as a number of homes in NSW were destroyed by bushfires.
The NSW Rural Fire Service has downgraded bushfires in Port Stephens in the state's Hunter region to `watch and act' levels, but warns a southerly change could spread the blaze.
"It can prove to be quite problematic because there's going to be extremely strong wind gusts that come with it," a spokesman told AAP on Sunday.
"When we get a shift from the wind and it turns south which we're seeing tonight, the sides of the fires can then turn into the fronts of the fires."
Five properties have reportedly been damaged or destroyed between Salt Ash and Tanilba Bay in Port Stephens.
"We don't have solid confirmation of that yet," the NSW RFS spokesman said.
"But obviously there's been footage on the news tonight which clearly shows there have been properties destroyed."
The fires across the state come as the Bureau of Meteorology issued a severe thunderstorm warning for the mid-north coast, the Hunter region and other parts of NSW.
The bureau is urging people in those areas to move their cars away from trees and stay indoors.
Conditions are easing on the Tangory Mountain fire ground, 15km east of Singleton but authorities warn the southerly change could make the situation worse.
Once the southerly change passes tonight, firefighters expect conditions to ease considerably. They'll use the calmer conditions in the next two days to contain the remaining fires.
More than 100 firefighters are also working on controlling a large bushfire in the Webbs Creek area, near Wisemans Ferry, in the Hawkesbury region.
Meanwhile, 43 cars were destroyed near Sydney Olympic Park in Sydney's west when a grass fire spread into a carpark near an aquatic centre, Fire and Rescue NSW Superintendent Ian Krimmer told AAP.
Around 1500 people were evacuated and three people were treated for smoke inhalation.
Authorities have declared the area safe but will continue to monitor it overnight.