An investigation was underway and many residents had been evacuated after the discovery of unknown, potentially hazardous material in the basement of a building in the Fenway neighborhood Tuesday night.

Streets were closed about a block in either direction around 76 Kilmarnock Street, and residents at a nearby home for seniors have been told to shelter in place, Police Commissioner William Evans told reporters Tuesday night. 

Investigators found a container filled with "some type of chemical," and other "gadgets" making up "some type of lab," Evans said. 

He said chemical tests were being conducted, and said the area would be re-opened once investigators determined there was "nothing sinister going on."

Police, Evans said, want to "err on the side of caution," particularly with a Red Sox game at nearby Fenway Park set to wrap up in fewer than two hours.