Police are searching for a motorcyclist over a deliberately lit grass fire in southwest Sydney as the state braces for a "pretty horrible" bushfire day.
A total fire ban is in place across NSW on Saturday, as firefighters continue to battle around 98 bushfires with temperatures expected to soar into the 40s in parts of the state.
Sixteen fires remain uncontained, with the biggest areas of concern at Yass, Deans Gap and Cooma, the RFS says.
In the early hours of Saturday morning, a woman spotted a small fire in Airds and a red motorcycle was seen leaving the area, police say.
The fire burned an area of grass about 24 sq metres.
Police are appealing for help in locating the motorcyclist.
It comes as a number of teenagers were arrested over deliberately-lit fires in southwest Sydney.
Two boys aged 17 and 12 were arrested following a grass fire at Eagle Vale on Friday, while a group of youths were spotted fleeing a string of fires at Macquarie Fields on Thursday night.
Two 16-year-olds were charged with breaching bail.
"We are looking at some pretty horrible conditions across the southern part of the state, but not all of the state," an RFS spokesman told AAP.
"We've got a grip on most of these fires and are doing some burning overnight to tie these fires in, but will be tested by the wind and weather conditions."