EAST BOSTON (CBS) — An apartment building was evacuated overnight after firefighters found increased levels of carbon monoxide there and in a courthouse next door, the Boston Fire Department said Monday.

Boston Fire responded to reports of a gas leak at the apartment building on Elbow Street around 10:50 p.m. Sunday.

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A CO leak in East Boston sent two people to the hospital Sunday night. (WBZ-TV)

A CO leak in East Boston sent two people to the hospital Sunday night. (WBZ-TV)

After the building was evacuated, four residents were checked out by Boston EMS, with two of them taken to an area hospital for further treatment. The other occupants of the building went to stay with family friends.

Next door, fire officials also found high levels of CO at the East Boston District Court building.

Boston Fire and Eversource officials said smoldering underground cables were the cause of the carbon monoxide. Investigators determined it was smoke from the electrical cable failure that tracked into those apartments and courthouse, setting off alarms.

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Eversource crews worked through the early morning hours to install new cables.

Eversource crews work to repair underground power lines Monday morning in East Boston. (WBZ-TV)

Eversource crews work to repair underground power lines Monday morning in East Boston. (WBZ-TV)

By 8:30 Monday morning, doors to the courthouse were open, right on time.

No word yet on when apartment residents will be allowed back into the building.

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