DERBY — Schools in the city were locked down Thursday morning after a bullet was found on a school bus, according to robocalls from Derby Middle School administrators.

No weapons were found.

The incident started while students were being dropped off at the middle school as classes were starting.

“The staff of bus 55 reported seeing a bullet on the bus floor after the students departed the bus,” according to a message from the administration.

The students from that bus were separated from the rest of the student population.

The riders from the bus were also separated from their belongings, such as backpacks, and each student “was met with individually,” according to a message from the school.

“Their backpacks as well as their lockers were checked and cleared. The Derby Police Department was on scene for safety and security and to assist in the investigation,” according to the message.

The lockdown was lifted at 10:30 a.m., after the school district sent a series of emails and robocalls about what was going on.

Derby Middle School is a sixth, seventh and eighth grade school. It is across a driveway from Derby High School, which was also put in lockdown during the investigation.

There was no word as of 1:40 p.m. June 5 about where the bullet came from or who left it there.

This story was updated several times June 5. Earlier versions are posted below.

DERBY — Schools in the city were locked down Thursday morning after two bullets were found on a school bus, according to a robocall from a Derby Middle School administrator.

Police were on scene at the middle school/high school campus on Chatfield Street as of 9:55 a.m. conducting an investigation, which included checking lockers in the middle school. Students’ bags were also searched.

The bullets were found on bus 55, according to the robocall. Middle school officials described the lockdown as happening out of an “abundance of caution.”

The middle school first sent word of the lockdown at about 8:38 a.m. — eight minutes into the start of the school day.

High school officials across the street sent an email at 8:46 a.m. saying that school was in lockdown as well.

At about 10:30 a.m., the principals at the middle school and the high school sent word that the lockdown had been lifted:

“Dear Parents and Community Members of DMS and DHS,

We want to provide you with a final update regarding the lockdown and shelter-in-place that occurred earlier today.

After two bullets were discovered on a school bus this morning, we immediately followed all safety protocols out of an abundance of caution.

Law enforcement and school administrators worked swiftly to investigate the situation, including a thorough search of students and school areas.

We are relieved to report that no weapons were found, and there is no ongoing threat to student or staff safety.

The investigation has concluded, and we have resumed all normal school activities for the remainder of the day.

We understand how unsettling these situations can be, and we deeply appreciate your patience, support, and trust as we prioritize the safety of every student and staff member.

We remain committed to maintaining a safe and secure learning environment and will continue to work closely with our local authorities.

If you have any questions or concerns, please don’t hesitate to reach out.

– Mrs. Caggiano and Mrs. Olson

That message was a series of messages administrators sent Thursday morning to keep parents in the loop.

The message below was received at 9:39 a.m.:

“This is Ms. Quartiano with a lockdown update. Out of an abundance of caution DHS and DMS entered into a lockdown due to a report of 2 bullets found on bus 55. While all students are in their classrooms and safe we are continuing lockdown until we are cleared to resume normal operations by Derby Police.”

At about 10:02 a.m., the middle school issued a robocall saying the building went from lockdown to “shelter in place,” which means students were back in classrooms while police continued their investigation.

“Additional information will follow once the investigation has been concluded,” according to the message.