An arsonist broke into a one-room Amish schoolhouse in the middle of the night and set a fire that caused an estimated $20,000 in damage.

Firefighters responded to the blaze at the Pleasant Valley School in West Earl Township shortly after 3 a.m. Saturday, according to Jonas Reiff, chief of the Farmersville Fire Company. The fire was put out in about 15 minutes.

Firefighters found that the school's doors were locked and also saw signs of a break-in.

Deputy State Police Fire Marshal James DeWalt ruled the fire was arson. DeWalt said there were no signs of vandalism and nothing appeared to have been stolen.

The one-room schoolhouse is attended by Amish and Old Order Mennonite schoolchildren in Lancaster County's Amish community. Classes there had recently finished for the year, Reiff said.

Police said they did not immediately have any suspects.

The building is less than 20 miles north of Nickel Mines, where a gunman shot 10 girls — five of them fatally — at an Amish school in October; he killed himself as police closed in.

The Amish community razed that school after the attack, opening a new one in April.