The U.S. Nuclear Regulatory Commission said Thursday that its staff are monitoring the situation at a nuclear power plant in South Carolina after the site lost offsite power Wednesday evening.

The commission said it is monitoring the event through its resident inspectors at the Catawba nuclear power plant, near York, South Carolina, and through its Atlanta regional office.

According to officials, one of the two units at the plant, operated by Duke Energy, was already shut down for an outage and the other unit automatically shut down after losing offsite power. The plant's diesel generators started to power the units' emergency loads.

Plant operators and other plant staff are monitoring the situation and attempting to restore power, while safety systems have operated as needed, officials said.

Duke officially notified the commission of the situation soon after the incident happened, and the regulatory agency's senior resident inspector was dispatched to the site. He has been able to observe plant activities and provide status reports to the commission staff manning the incident response center in Atlanta.

Duke declared the unusual event as the lowest of the four emergency classification levels of the commission.

The commission said there was no radiation released or impact to plant workers or the public, adding that it will review the cause of the incident and determine if additional inspections or follow-up are needed.