A squirrel caused a disruption in a South Portland substation that knocked out power to thousands of customers and closed schools in South Portland and on Peaks Island on Thursday.

The outage impacted more than 5,300 customers in South Portland, 200 customers in Cape Elizabeth and 1,400 customers in Portland early Thursday morning. Power was restored by around 11 a.m. after repairs were made at the Central Maine Power substation on Highland Avenue.

Catharine Hartnett, a company spokeswoman, said a squirrel caused the disruption inside the substation. The process of finding and repairing the damage can be lengthy because substations are highly energized and dangerous facilities and the recovery work needs to be done methodically, she said.

Peaks Island School was closed Thursday because of the power outage, as were all schools in South Portland.

“Since most of the city is currently without power, we are unable to hold classes remotely. We are aware that more than one third of homes and five out of eight schools are without power,” South Portland Superintendent Ken Kunin said in an email to parents.

Kunin said all of the city’s schools were without phone or internet service.

South Portland schools were not be able to serve meals and students were told to use storm packs that had already been sent home, Kunin said.

Animals account for 15 to 20 percent of CMP power outages each year, Harnett said. Most of those cases involve squirrels on the transformers on utility poles.

“To address that challenge we are adding ‘animal guards’ to these pole-top transformers that prevent the animals from making contact and causing localized outages. We installed over 10,000 in 2020 and intend to nearly double that number in 2021,” Hartnett said.