There is no emergency, officials said, and the public needs no protective action.
A Duke Energy spokesperson told ABC11 the plant is operating safely.
According to the Chatham County Public Health Department's spokesperson, emergency management directors for the state, alongside Wake, Harnett, Lee, and Chatham counties, were notified about the siren alert. The system within the 10-mil emergency planning zone of Duke Energy's Shearon Harris Plant was activated at about 8 a.m.
Sirens will be tested on Wednesday, as planned.
Fisherman Steve Ellis, who was on the water nearby at the time of the sirens, said he got the alert on his phone. He never heard the actual alarms.
"I was gonna fish until it was over," he said. "I wasn't too worried 'cause you didn't see the flares."
ABC11 is working to learn what triggered the alarm.