A New Jersey elementary school closed on Thursday due to a fungus build-up in the building, district officials said.

More than 250 student at Willow Grove Elementary School in Hackettstown got the day off while workers took samples, dehumidified the building and replaced or cleaned ceiling panels, white boards and other fungusy items in classrooms.

Superintendent Dave Mango said that while officials didn't think the fungus was harmful, he didn't want to take any chances with the substance found in 13 rooms in the building.

"It's unfortunate, but we want to be safe rather than sorry," he said.

Mango said that a maintenance worker spotted fungus on a blackboard and ran it up the chain of command when he tried unsuccessfully to clean it. A test revealed that the fungus wasn't dangerous black mold, but Mango and district officials decided to thoroughly clean the building, which was built in 1971 and has had issues with poor ventilation and high humidity.

The abrupt closing left families scrambling to make alternate child care arrangements. At least one mother off from work for Rosh Hashanah offered to take in other families' children, and others took their kids to the nearby Riverfront Park to enjoy the warm -- and unexpected -- school holiday.

Ashley Story, a third-grader at Willow Grove, told News 4 that she'd rather be in class than on the jungle gym, but emphatically said "No!" when asked if she wanted to be somewhere where fungus was growing.

Her mom, Stephanie Story, meanwhile said she was glad that the district took a decisive action.

"We're not sure what's in the walls in the classroom so this is the best thing to do," she said.

The school building will be closed through at least the end of the week -- but students will report to Hackettstown Middle School on Friday. Afterward, they could be placed in other schools until the school is completely clean.

It's not clear when the students will be back in their old classrooms at Willow Grove.