MANNINGTON TWP. -- A message sent out Tuesday night that there was some type of incident at a Salem County nuclear plant was a mistake, officials say.

"There is no nuclear emergency at the plant," said Brenda Banks, spokeswoman for Salem County.

The State Office of Emergency Management posted the alert in error during a routine drill that was being conducted, according to Banks. Salem County officials were not responsible, she said.

There is NOT an emergency at the Salem Nuclear plant. Any message received is an error. — Salem County OEM (@SalemCountyNJ) May 24, 2017

The mistaken alert went out shortly before 9 p.m. Afterwards, in Salem and Cumberland counties, a reverse 911 call was put out alerting residents that there was no emergency at the nuclear generating complex in Lower Alloways Creek Township.

"We are conducting an emergency drill. Some of the drill scenario was mistaken for an actual emergency," said Joe Delmar, spokesman for PSEG Nuclear, Tuesday night. "We are working with the New Jersey Office of Emergency Management to correct this information. Again, there is no emergency."

Banks said that once the mistake was noticed, officials began getting out the word to the public and the news media that all was OK.

Had there been an actual emergency, the nuclear emergency warning sirens in New Jersey and Delaware within the 10-mile radius of PSEG Nuclear's Artificial Island generating complex would have been sounded.

In Tuesday night's case they were not.

The drill is part of the overall planning for how to react to an actual problem at the plants. Drills are conducted annually so that emergency management officials at all levels are prepared.

This year the drill centered around a scenario that something had taken place at the Hope Creek reactor. Hope Creek is one of three operated by PSEG.

After the alert went out, social media immediately lit up with people worried that something dire had happened.

***FALSE EMERGENCY ALERT*** You may have seen this message on your TV tonight.There is NO emergency. This message went out in error #ReadyNJ pic.twitter.com/qzh0l9rZ03 — NJOEM (@ReadyNJ) May 24, 2017

How the message was mistakenly sent was not immediately clear.

The state Office of Emergency Management falls under the jurisdiction of the New Jersey State Police.

An operator at State Police headquarters Tuesday night also confirmed that the alert was a mistake.

Along with Hope Creek, PSEG Nuclear operates the Salem 1 and Salem 2 at the Island. The plants comprise the second-largest commercial nuclear generating complex in terms of electricity output in the U.S.

They are located along the Salem County shoreline where the Delaware River meets the Delaware Bay.

The three plants are among the four operating in New Jersey. The other, Oyster Creek, is located in Ocean County.

The utility and state, county and local emergency management officials have detailed plans in place of what to do should there be an actual emergency at one of the plants.

Banks said officials were still trying to determine what happened. They expect to continue investigating into the incident on Wednesday.

Most of the team involved with the drill was on site at the at Salem County Office of Emergency management headquarters on Cemetery Road in Mannington Township, the same location they would gather in the event of an actual emergency.

Bill Gallo Jr. may be reached at bgallo@njadvancemedia.com. Follow Bill Gallo Jr. on Twitter @bgallojr. Find NJ.com on Facebook.