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ST. LOUIS, MO (KTVI) – An underground electrical vault caught fire under the US Bank building in downtown St. Louis.

Firefighters said an internal problem in an electrical transformer caused the explosions. Ameren workers are using cutters to remove the transformer that caused so much fear.

Neil Elias works for US Bank. “You could tell there was all kinds of smoke outside the building and actually you could smell the smoke inside the lobby,” Elias said. “I just heard three booms.”

Fire and smoke filled the air around U.S. Bank Plaza as people were forced out of the building.

Ryan Kemer works for Thompson Coburn, which is in US Bank Plaza. “I was at my desk and heard three loud explosions,” he said.

Firefighters say an electrical transformer in an underground vault on 7th Street exploded around 5 Tuesday afternoon. Fortunately no one was walking near the vault.

The explosion knocked out power in the 36 story building, leaving at least ten people trapped in elevators.

As fire and smoke continued to shoot out of the vault, firefighters rushed to rescue the trapped people and clear the rest of the building.

Around 6:30 p.m. firefighters used a dry chemical to smother the electrical fire.

But the smoke still lingered, as will the memory of the explosions.

No injuries were reported. Power is still out in the south side of the building, but crews are working overnight to fix that so people can return to work.