A four-block area of downtown Bluffton, including the Wells County Courthouse, was evacuated Tuesday after an underground natural gas line was damaged.

The gas main, in the 100 block of Johnson Street, was damaged sometime after noon as city water department crews worked to repair a water main break, Mayor Ted Ellis said.

Ellis said crews initially thought the main was undocumented, as NIPSCO officials had already marked the known gas lines in the area before digging began.

NIPSCO spokesman Nick Meyer said it was premature to comment on what might have led to the main break. An investigation will be made after repairs are completed on the gas line, he said.

“They will do a root cause analysis to make a determination of how it occurred,” he said.

Officials have not determined whether the gas line was properly marked, he said.

The Courthouse, which had about 30 employees inside, was evacuated about 1:30 p.m. after a decision by the county commissioners, Ellis said. Children normally dropped off after school by buses in that area were instead dropped off at the City Gym within City Hall, Ellis said.

About 25 to 30 gas customers, mostly residential, lost service Tuesday afternoon.

Service was expected to be returned to those customers by nightfall, Meyer said.

“It’s a very intricate system, very similar to a spider web,” he said. “There are lines running throughout places you would not normally expect.”

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