Pennsylvania Gov. Josh Shapiro and his family were evacuated overnight from the official governor's residence after someone set fire to the building, police said Sunday.

No one was injured and the fire was extinguished, according to authorities.

The fire broke out overnight on the first night of the Jewish holiday of Passover, which Shapiro and his family had celebrated at the governor's official residence in the state capital of Harrisburg. Pennsylvania State Police said in a statement that, while the investigation was ongoing, they were "prepared to say at this time that this was an act of arson."

State police gave no other details about the cause of the fire at the riverfront mansion but said it caused a "significant amount of damage" to a portion of the residence. Shapiro and his family had been in a different part of the residence, police said.

In a statement, Shapiro, viewed as a potential White House contender for the Democratic Party in 2028, said he and his family woke up at about 2 a.m. local time to bangs on the door from the Pennsylvania State Police after the fire broke out.

The Harrisburg Bureau of Fire was called to the residence and, while they worked to put out the fire, police evacuated Shapiro and his family from the residence safely, Shapiro said.

"Thank God no one was injured and the fire was extinguished," Shapiro said in a statement.

On Sunday, fire damage was visible on the residence's south side, primarily to a large room often used for entertaining crowds and art displays. There was still a police presence early Sunday afternoon as yellow tape cordoned off an alleyway and an officer led a dog outside an iron security fence.

Shapiro splits his time between the mansion that has housed governors since it was built in the 1960s and a home in Abington, about 161 kilometres east. He posted a picture on social media Saturday of the family's Passover Seder table at the residence.

State police are leading the investigation. The agency offered a reward of up to $10,000 US for information leading to an arrest and conviction.