The discovery of a clandestine lab forced evacuations and the closure of busy streets in the heart of a Vermont city.
Winooski Police would not say what the lab was allegedly being used for, but told reporters no explosions happened and that no one suffered any injuries.
Investigators said more information on the case would be available Wednesday morning.
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During the investigation of the accused lab, public safety officials evacuated several nearby buildings that house apartments and restaurants, several of which were unable to operate.
A shelter was set up for people who were evacuated, city officials said.
During the work, which acting Winooski city manager Ray Coffey described as "decontaminating" the apartment that was home to the lab, police blocked off part of the Winooski traffic circle.
The move stopped traffic from going over the bridge to Burlington, and forced drivers to detour.
"I think any time with a situation like this, safety's paramount, especially when you're dealing with a dense area like this," Coffey said, referring to the decision to evacuate the area around the clandestine lab. "We didn't want to mess around with any risks."
The Vermont Hazardous Materials Response Team arrived late Tuesday afternoon and determined there was not a threat to the public, Coffey said.
Residents stayed out of the area while the decontamination work continued.