Law enforcement agencies were searching late Thursday for a Brazilian man who escaped from a prison near Philadelphia days after he was sentenced to life in prison for the fatal stabbing his girlfriend, the authorities said.

The inmate, Danelo Cavalcante, escaped from Chesco Prison in Chester County on Thursday morning, the local district attorney’s office said on X, formerly known as Twitter.

Deb Ryan, the Chester County District Attorney, told reporters that Mr. Cavalcante was last seen walking southbound in the county’s Pocopson Township on Thursday morning wearing a white T-shirt, gray shorts and white sneakers.

“If you see him, do not approach him,” Ms. Ryan said at a news conference. “We’re asking you please to contact 911. He is considered extremely dangerous.”

The district attorney’s office did not immediately respond to requests for comment late Thursday. Chester County lies just west of Philadelphia.

Mr. Cavalcante, 34, is a Brazilian national who is also wanted for homicide in Brazil, the United States Marshals Service said in a notice.

Last week, Mr. Cavalcante was sentenced to life in prison without parole after being convicted of first-degree murder. The district attorney’s office has said that in April 2021, he stabbed his girlfriend, Deborah Brandao, to death in front of her children, ages 4 and 7. Mr. Cavalcante, who was living in Royersford, Pa., at the time, fled the murder scene and was arrested hours later in Virginia.

Before the attack, Ms. Brandao had learned of Mr. Cavalcante’s open warrant for murder in Brazil and threatened to tell the police, according to the district attorney’s office. “Detectives determined that this was the motive for the murder,” the office said in a Facebook post last week.

This is a developing story.