Basin Electric Power Cooperative spokesman Floyd Robb said the power plant itself, just southeast of Stanton, was not affected by the blaze.
Robb said the fire started in a building being used to make Fiberglas liners for a new plant smokestack as part of a pollution control project.
The cause was being investigated.
Mercer County emergency manager Richard Sorenson said at midnight that firefighters reported making progress against the fire, despite windy conditions. Gusts of more than 30 mph were reported in the area during the night.
"It's still burning, but they've been able to knock it down somewhat," Sorenson said around midnight. "There's a rail tanker car in the area. They've kept it cool and they don't feel it's in any danger."
Sorenson said the building contained a number of chemicals and the area downwind of the site was evacuated as a precaution. He estimated about a dozen people were forced to leave.
Robb said no one was in the building when the fire started.
State Highway 200A was shut down from the junction of State Highway 48 to the junction of Highway 31 north of New Salem.