Montgomery County officials say a middle school has been evacuated for an undefined cause that was originally thought to be a possible carbon monoxide leak.

It happened around 10:45 a.m. Thursday at Pottsgrove Middle School at 1351 N. Hanover Street in Upper Pottsgrove Township after an alarm went off.

Map: Pottsgrove Middle School

Officials said 23 students became sick and were taken to the hospital but there is no word yet on their conditions.

The school was evacuated and crews are checking the building.

School officials said the students who weren't sick were taken to the high school, but are asking that parents not pick up their children until attendance can be verified.

Parents are encouraged to check the school district's website and Pottsgrove Facebook page for updated announcements.