NEW YORK (CBSNewYork) – Several NYPD officers are recovering after being exposed to a dangerous narcotic during a drug bust in the Bronx.

It’s unclear exactly what the substance was, but police said it may have been fentanyl or heroin.

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Officers raided an apartment around 7:40 p.m. Thursday on Willis Avenue near 140th Street in the Mott Haven section and took several people into custody.

“We heard a big bang, police ‘open up,’ they raided in, flash grenade, boom. Next thing you know, they’re taking out people,” a neighbor who lives across the hall told CBS2. “It was a little scary.”

“I heard the cops screaming. Just broke the door down,” neighbor Eddie Serrano said.

“I’ve never seen anything like this before,” said neighbor Jackqueline Allen.

The building was evacuated for some time before residents were allowed to return. Neighbors who have lived there for decades said a quiet family lives in the apartment.

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“They have a son, they have a daughter… They always seemed nice,” the woman who lives across the hall added. “Goes to show you don’t know who you know.”

“I was shocked,” Serrano said. “I never knew they were going to be like this. They’re good people.”

“I just heard from the other neighbors that they was up there bagging heroin,” said Allen. “You never know who’s in your building, who lives there.”

Five officers were hospitalized overnight but have since been released. One reported feeling side effects, but no one was hurt.

Seven people – six men and one woman, ages 35 to 59 – were arrested on charges of reckless endangerment and criminal use of drug paraphernalia. Two of them were also charged with resisting arrest.

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Authorities said they could face federal charges, as well.