(CNN) Eighteen-year-old Elias Ali was stocking shelves at the Karibu Grocery and Deli in St. Paul, Minnesota, when it suddenly shook Friday morning.

Posters fell off the wall. Ali said he and others thought the violent vibration was an explosion, but weren't sure if it was in the building.

"By the time we figured out everything inside was OK, we went outside and saw the home had exploded," he said. "We were devastated, because we live a block away and it could have been ours."

Authorities are trying to figure out what caused the explosion the morning after Thanksgiving.

Surveillance video shows the quiet street when flames suddenly burst into the air, sending debris flying everywhere.

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