Pennsylvania state authorities have arrested a 38-year-old Harrisburg man and said he set fire to the Pennsylvania governor’s mansion, forcing Gov. Josh Shapiro and his family to evacuate early Sunday before the blaze severely damaged part of the building.

The man, identified as Cody Balmer, 38, jumped a fence and managed to evade state troopers as he broke in to the building and set the fire, the authorities said, adding that he had used homemade incendiary devices. He fled the scene and was arrested in Harrisburg on Sunday afternoon, officials said in a news conference.

Mr. Balmer is in custody and is expected to be charged with attempted murder, arson and terrorism. Law enforcement officials said they could not provide any information about a motive.

During the news briefing outside the mansion, Governor Shapiro, a Democrat who gained national prominence last year when he was on the short list of possible running mates for Kamala Harris, said that the F.B.I. was helping in the investigation.

Mr. Shapiro, who became emotional as he described his family’s ordeal, recalled the moment a state trooper banged on his door shortly after 2 a.m., woke him, his wife and children, and rushed them to safety from an arson attack that he called “targeted.”

“Last night, we experienced an attack, not just on our family, but on the entire Commonwealth of Pennsylvania,” Mr. Shapiro said, with the blackened, broken windows where the arsonist struck behind him. “I want you all to know that your prayers lift us up, and in this moment of darkness, we are choosing to see light.”

“This type of violence is not OK,” Mr. Shapiro added, his voice rising in anger. “I don’t give a damn if it’s from one particular side or another. It is not OK. And it has to stop. We have to be better than this.”

The State Police said in a statement that the fire caused “a significant amount of damage to a portion of the residence.”

Hours before the fire, Mr. Shapiro, who also has a home north of Philadelphia, wrote on social media that he and his family were marking Passover, which began at sunset on Saturday.

Images posted on social media showed firefighters battling the fire. A portion of the mansion was obscured in dark smoke, and some windows were shattered.

Bryan Flores, 37, a neighbor who lives across the street from the residence, said he awoke shortly after 2 a.m. to see a large response outside from the police and firefighters. “We woke up to the sirens and the flashing lights and stuff,” Mr. Flores said. He added that the incident seemed under control at that point.

Mr. Shapiro, who served for six years as the state’s attorney general before being elected governor in 2022, has been the target of threats at least once before. In November 2023, the police arrested a man who they said sent a threatening email to him, according to a Pennsylvania State Police report. It was unclear on Sunday if the man was charged in connection with that incident.

The governor’s residence is a 29,000-square-foot Georgian-style building on the Susquehanna River that was completed in 1968, according to the state government. Its landscaped grounds occupy a full block about a mile and a half from the State Capitol complex.

The public is able to tour the residence, which exhibits art and artifacts on the first floor.

Recent high-profile incidents of violence directed at political figures have helped fuel fear and unease among Americans, polls have shown. Before the presidential election last year, about four in 10 voters said they were extremely or very concerned about violent attempts to challenge the outcome. The assassination attempt against President Trump last summer took place in Butler, Pa., a little over 200 miles west of Harrisburg.

Other serious incidents have included a foiled plot to kidnap Gov. Gretchen Whitmer of Michigan in 2020, and the home invasion and assault at the home of Nancy Pelosi in 2023, which seriously injured the former House speaker’s husband, Paul.

Though American politics has grown increasingly acrimonious and deeply polarized in recent years, research shows that extremist violence in the United States has actually declined, even though a handful of episodes have drawn widespread attention and alarm. Scholars who study the issue have said that the political climate has not become more broadly violent.

Campbell Robertson, Amanda Holpuch and Allison Beck contributed reporting. Susan Beachy contributed research.