NSW Rural Fire Service Commissioner Rob Rogers on Wednesday warned wet conditions had boosted grass growth across the state while bush regeneration from the Black Summer bushfires was occurring faster than predicted.
He said while the forecast was for more rain, it would only take a "matter of weeks" for dry conditions to ramp up the danger of bushfires this season.
Mr Rogers said a significant grassfire season could come over the next two summers.
"It absolutely will happen," he said at RFS headquarters in Sydney.
"While it's been wet we don't want people being complacent. Sooner or later ... we're in for a big grass fire season."
Asked if a big grass fire season could come as soon as this season, Mr Rogers said, "If it stops raining, absolutely".
He said the threat of grassfires was increased by the state's cold winter, which had seen the excess build-up of grass hit by frosts, increasing fire risk.
"It doesn't need to dry off as such," Mr Rogers said.
The warning comes as authorities work to prevent a repeat of the devastating 2019-20 Black Summer bushfire season, the worst on record in NSW.
Over the course of that summer, 26 lives were lost, 2448 homes were destroyed and 5.5 million hectares of land was burnt.
Also on Wednesday, the RFS launched the new Australian Fire Danger Rating System, simplifying fire warnings with practical calls to action for communities.
The new AFDRS reduces the number of warning levels from six to four to provide national consistency for fire alerts.
From Thursday, risk levels used by fire authorities will be moderate, high, extreme and catastrophic, which means "For your survival, leave bushfire area".
The new ratings replace previous advice of low-moderate, very high and severe.
Mr Rogers said he was "absolutely" confident the new system would meet a recommendation from the royal commission into the Black Summer bushfires, which urged national consistency in fire warnings.
"The new fire danger rating system will give people living, working and travelling in bushfire-prone areas clearer and more accurate information about the risk they face," he said.
"The new ratings will be displayed in communities across the country from tomorrow, such as on websites, smartphone apps, social media and on roadside signs."
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