All Long Beach school district buildings were under "lockout" Thursday morning as police investigated the credibility of a potential threat, officials said.

In a statement, schools Superintendent Jennifer Gallagher said the lockout would be lifted at noon for all buildings except the high school, which will be under a "modified lockout" for the remainder of the day.

Students and staff will be permitted to enter the high school, Gallagher said, and police would remain at the school through dismissal. 

In a separate email, sent earlier in the day, Gallagher told parents that students and staff were safe.

“Long Beach police notified us of a threat that they believed warranted a 'lockout' (meaning no one can come in) at Long Beach High School as a precaution,” she wrote. “The police are there now and are investigating the source of the threat to determine whether or not it is credible."

A Nassau police spokesman said the lockout was done “out of an abundance of caution” and noted that there was no active threat to students. He could not immediately elaborate on the nature of the threat.

Check back for updates on this developing story.