A 17-year-old volunteer firefighter has faced court after allegedly sparking a series of bush fires in Sydney's west that he later helped put out.

The teenager was arrested and charged after detectives identified a "pattern of deliberately lit bushfires" in the Wallacia area on the city's western outskirts between June 23 and September 7 this year, a NSW Police statement said.

The arrest was part of Strike Force Tronto - an ongoing arsonist probe led by State Crime Command’s Financial Crimes Squad Arson Unit.

The teenager allegedly lit a string of fires before responding to each one in his role as a volunteer firefighter.

Investigators identified the alleged firestarter with assistance from the Rural Fire Service.

He was arrested by detectives in Warrimoo about 7am on Thursday before

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