NYPD Police Officer Jason Rivera is getting a hero’s farewell at St. Patrick’s Cathedral.

Thousands watched as the slain young cop’s body arrived Thursday at the historic Manhattan church in a police motorcade for his wake, ahead of Friday’s funeral service. 

A phalanx of New York’s Finest stood at attention in dress uniforms, as eight pallbearers carried Rivera’s casket up the steps and bagpipers pierced the silence with a moving rendition of “Amazing Grace.”

Church bells tolled as a second motorcade arrived with Rivera’s grieving family for a private viewing before the doors opened to the public.

Inside, the body of the 22-year-old cop lay at the foot of the altar with his photo alongside an NYPD flag made of flowers. 

“His family is just devastated,” Jay, a childhood friend of Rivera’s, said outside the cathedral. “He was kind, smart and always happy. He was full of life. He never had a problem with anybody.”

By the time the doors opened to the public shortly before 1:30 p.m., the two-deep line of mourners — most of them first responders — ran the length of block on East 50th Street and around the corner.

Police officers from around the world were among those who attended.

“We all bleed blue, no matter what police department you’re from,” Miami, Florida, Police Officer Rebecca Olmedo said. “We’re all brothers and sisters in blue. And we all have families that we do our best to go home to.”

Detective John Sullivan, with the Chicago Police Department, also showed up to the wake. 

“It’s a tragedy we all feel,” he said outside the church after the viewing. “It’s a shock that something so violent can happen to two guys who just wanted to do the right thing.”

Ronnie Anderson, a sergeant with the Dallas Police Department added: “We just wanted to come up here and pay our respects to the families and let them know we’re behind them.”

Mayor Eric Adams and NYPD Commissioner Keechant Sewell were among those who paid their respects, but used a side entrance and did not comment.

“It’s heartbreaking,” Queens resident Kathy Geraghty said outside the cathedral Thursday morning, hours before the 1 p.m. wake.

“I went to say a prayer and light a candle for the two police officers and their families,” Geraghty said with tears in her eyes. “It’s a crazy world we live in. There’s no law and order, despite police trying their best.”

Nina Chatman, 67, of Brooklyn, said she also came to pay her respects.

“He was just a baby,” Chatman said. “I didn’t know him, but I know he was somebody’s son. When I saw his smiling face in the newspaper it broke my heart, because I knew he was a good person.”

Rivera’s body was taken from an upper Manhattan funeral home through the streets of Manhattan in a huge police motorcade to Midtown.

Just before 8 p.m.,the slain officer’s family emerged from the church, embracing in hugs on Fifth Avenue. 

Rivera’s partner, Wilbert Mora, is due to be mourned next at a funeral at St. Patrick’s next week.

Rivera’s wake will be followed by a funeral service on Friday and a private cremation ceremony at Ferncliff Cemetery in Westchester County, officials said this week.

Rivera, a 22-year-old newlywed, was killed when deranged career criminal Lashawn McNeil ambushed the him and officer Mora during a domestic violence call in Harlem on Friday.

Mora, 27, was pronounced dead from his wounds in the attack on Tuesday.

The bodies of both officers were taken to Riverdale Funeral Home in Upper Manhattan this week pending their funerals.

McNeil was shot by a third officer, rookie Sumit Sulan, during the attack on Rivera and Mora and died from his wounds earlier this week.

Rivera and Mora are the first NYPD officers killed in the line of duty since April, when officer Anastasios Tsakos was struck and killed by a drunk driver at the scene of an accident on the Long Island Expressway.