(CNN) -- A nuclear power plant 19 miles north of Omaha, Nebraska, declared an alert due to electrical problems, officials said.

The Nuclear Regulatory Commission said Tuesday morning's incident was "declared due to an indication of fire." But Omaha Public Power District, which operates Fort Calhoun Station, said the alert was due to smoke and there was no indication of fire.

The fire was extinguished within 50 minutes, the NRC said, adding an "alert" is the second-lowest of four emergency classes.

"There was no danger to the public of a radiation release because the plant has been shut down since early April for a refueling outage and remains in that condition," the NRC said in a statement Wednesday. "Although the plant briefly lost its normal ability to cool the spent fuel pool, temperatures in the pool remained at safe levels and the plant recovered pool cooling without the need for any of the plant's multiple backup systems."

The NRC said it monitored the situation.

In a statement late Tuesday, the Omaha Public Power District said the alert resulted from smoke in an electrical switchgear room.

"After a thorough safety review, the plant was cleared to return to its level one emergency that was declared Monday due to flood conditions," the customer-owned utility said.

Fort Calhoun Station has been down since April 9 for a refueling and maintenance outage. It remains shut due to flooding on the Missouri River.