A volunteer firefighter is accused of deliberately lighting more than a dozen bushfires, some of which he was later involved in trying to put out.
Arson detectives earlier this month began investigating a series of suspicious fires across the NSW Hunter region.
On Wednesday, investigators arrested 18-year-old Jack Hardidge at his Aberglasslyn home shortly after 8am on Wednesday.
The teenager appeared at Maitland Local Court on Thursday and was refused bail.
Police allege Hardidge deliberately lit fires in grassland at Weston, Pelaw Main, Bellbird, Greta, Aberglasslyn, Melville and Cessnock on several occasions in July and August.
He later attended some of the fires as a Rural Fire Service volunteer and helped extinguish the blazes, police said.
Hardidge has been charged with 15 offences, including 13 counts of intentionally causing a fire and being reckless as to its spread, and two counts of destroying property using fire.
Police allege a vehicle was damaged in one of the fires, as well as a large number of tires.
Investigators are still looking into the possibility that another person was present when Hardidge allegedly lit some of the fires.
Acting Detective Superintendent Richard Puffett said police were still exploring the motive behind the teen's actions.
He urged members of the community to report any suspicious activity taking place in bushland to police.
"Whether that be vehicles or persons that don't appear to be having a purpose, or being in the wrong place at the wrong time," Det Supt Puffett said.
"Even if you think it's small ... we will act on it."
The case is due to return to court on September 13.