An Eversource worker was injured and power was shut off to thousands of customers in Newton Monday when an explosion and small fire took place at a power substation across from City Hall, according to the Newton Fire Department and the company.

The worker was being treated for “non-life threatening injuries” that included apparent burns to both of his arms and his head at Massachusetts General Hospital, officials said.

The worker is in his 40s, according to Newton Fire Department spokesman Lieutenant Michael Bianchi. He said firefighters were alerted around 10:30 a.m. to an “explosion” at the Eversource facility at 375 Homer St., across from City Hall.

Two workers, including the injured worker, were the only people in the facility at the time, he said. Arriving firefighters discovered the injured worker and a high level of carbon monoxide inside the facility. Air quality has since returned to safe levels, he said.

Bianchi said the cause of the explosion and how the worker was injured is an issue that Eversource is in charge of investigating.

In its statement the company said “an equipment issue at one of our substations in Newton caused a small fire on our property and a power outage.”

Some 2,500 customers were without power in the immediate aftermath of the incident, but the utility has since reduced the outage to about 1,000 customers. Restoration efforts are continuing, the company said.

“Our crews will work to restore power to all remaining customers as quickly as safely possible and will investigate what caused the equipment issue,’' the company said in a statement.

John R. Ellement can be reached at john.ellement@globe.com. Follow him on Twitter @JREbosglobe.

Work at Boston Globe Media