Over 75 wildfires have been reported burning across the Australian state of New South Wales (NSW) on Sunday, with the return of extreme heat and strong winds.

NSW Rural Fire Services (RFS) called on local residents to remain vigilant to any fire threat and to follow safety protocols, as multiple regions across the state saw their maximum temperatures exceed 30 degrees Celsius and even near 39 degrees Celsius.

"As of 2:30 p.m. local, there are over 75 fires burning across the state, with 30 not yet contained. Two fires are currently burning at a Watch and Act status," the rural fire authority said, noting that more than 800 firefighters and specialists are working to contain the blazes.

Across NSW, 18 out of 21 weather areas have been forecast to confront high to extreme fire danger during the day. Total fire bans are now in place for nine areas.

After some cool relief over the past weekdays, the Australian Bureau of Meteorology (BOM) issued fire weather warnings for NSW on Sunday.

"Hot, dry, and windy conditions are forecast today across NSW, elevating the fire danger as temps reach the mid-30s," the weather bureau noted.

BOM Forecaster Jake Phillips told local media that the sweltering temperatures are likely to drop from Sunday night.

"Monday's temperatures will be a little bit cooler but a brief respite as Tuesday weather heats up," Phillips added.

Sunday also marks the official start of the 2023-24 bushfire season, with most local government areas in NSW commencing their statutory Bush Fire Danger Period, which would run through to March 31, 2024.

In September alone, NSW RFS responded to more than 2,000 bush and grass fires across the state due to unseasonably warm weather in early spring.

"The fire activity over recent weeks is likely to be a prelude of what we can expect to see this fire season. After years of wet weather and floods, we need the community to focus again on the risk of bushfires," said NSW RFS Commissioner Rob Rogers.