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Crews were still working at a Lexington, Massachusetts, substation Tuesday morning after a transformer explosion sparked a multi-alarm fire on Monday.

A photo shared with NewsCenter 5 showed the explosion off Massachusetts Avenue in downtown Lexington, not far from the post office. The explosion resulted in a three-alarm fire in the 1700 block of Mass. Avenue, with thick, black smoke pouring into the air.

"I was shaking. I'm still shaking. It was terrifying," said witness Emerson Graf. "We started to hear scratching and little clicking noises and we just looked over and there was this giant explosion. We didn't know what happened. It was just insane. It was so loud."

The transformer fire led to streets in the Lexington Center area being closed to vehicle traffic. Police said they also closed the Minuteman Bikeway.

Lexington Fire Chief Derek Sencabaugh said the substation where the transformer explosion happened belongs to Eversource Energy.

An Eversource spokesperson said the fire was reported just before 6 p.m. and that there were no power outages associated with it.

Firefighters poured water on the 16-foot transformer for about an hour, battling both the blaze and high temperatures.

Tuesday morning, repairs and the investigation were still ongoing.

"Our crews are still assessing what caused (Monday's) transformer fire at our substation off Mass. Ave. in Lexington," Eversource said in a statement. "The fire caused damage to some of our equipment and in order to begin working on repairs, it was necessary to switch approximately 50 customers in the area to generator power overnight. Once we complete those repairs, all customers will be switched back."

On top of trying to keep the crews as cool as possible, Sencabaugh said another big concern Monday night was water getting into the switchers in the basement of the substation. Those switchers are more than 100 years old.

"Because if the water had come up, it would start popping switches, which would then pop manholes down the street. So we, initially, were really starting to push people out of the area," Sencabaugh said.

No injuries were reported in connection with the fire.

Sencabaugh said one possibile cause could be the high demand for electricity to power air conditioners given the high temperatures and humidity levels over the past several days.

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