SAN JOSE — A longtime San Jose firefighter was arrested at the station where he worked Thursday afternoon and is facing drug and sex crime charges involving children, according to the state Department of Justice.

Mario Enrique Cuestas, who has worked with the department for decades, is being charged with the sale and possession of methamphetamine as well as sex assault and oral copulation charges with minors, according to DOJ spokeswoman Michelle Gregory.

“We believe he was providing drugs to minors, and soliciting them through websites,” Gregory said.

Cuestas, 53, was booked into Santa Clara County Jail after being arrested without incident at his workplace, Gregory said. No bail was set as of late Thursday.

Gregory did not know the number of possible victims or how long the crimes may have been going on, but said “there could be more that come up. It’s an ongoing investigation.”

“We just don’t know yet,” she said. “We need to go through everything to see if there’s more there than we know about.”

She said the matter came to light through a tip.

“I don’t believe it came from a minor,” she said. But when officers in a DOJ task force took up the case, “we were able to find out more about what he was doing.”

Gregory said computers and records were seized both at the fire station where Cuestas works and at his home, which is listed as being in San Lorenzo. According to his Facebook page, Cuestas has been with the San Jose Fire Department since 1994 and also worked for the Roman Catholic Diocese of San Jose since 2012 as a church singer.

Contact Eric Kurhi at 408-920-5852. Follow him at Twitter.com/erickurhi.