An apparently homeless man died Tuesday after he set himself on fire on the steps of a Manhattan church, collapsing on the street in front of horrified onlookers, cops said.

A witness called 911 to report that the 48-year-old man had set himself ablaze around 2:30 a.m. at East 16th Street and Rutherford Place, a tree-lined corner that is home to St. George’s Episcopal Church, police said.

Disturbed onlookers standing about 50 feet away told cops the man said nothing as he sparked the deadly blaze and then fell to the ground.

Video of the horror, viewed by a church worker, shows the fire starting small – beginning at the top of the steps in the corner near the door. 

“When he was coming down the steps the fire got bigger and bigger,” the worker, who did want to give his name, told The Post.

“When he came down, he stood still,” the worker added. “He stood there as the flames were growing and growing. The flames were going up – from his waist up. He was burning. Then he walked across the street.”

The employee said the burning man’s calm demeanor “blew [his] mind” – and he never reacted “like he was in pain.”

“He didn’t run. I can’t believe he walked,” the stunned employee recalled. “When I see the person on fire, there was a moment when he was calm. He probably was on something.

“For him to be able to remain that calm, he had to be on something major, major. You don’t see the effort of him trying to stop it.”

The worker said he wished he had been there to help the man – and even fight him to stop him from hurting himself.

Another church maintenance man who watched the video said “the fire was just shooting up,” and the man who started it was alone at the time.

“I don’t like to see something like that,”he said. “It’s sad. Why did he do that to himself?”

The unconscious and unresponsive man was pronounced dead on the scene by responding EMS workers. 

His name has not yet been released, pending family notification. 

It was not immediately clear how the man had set himself on fire, and the investigation is ongoing, cops said.

A white sheet, crime scene tape and evidence markers could be seen just outside the church in the aftermath. Stuyvesant Park, as well as a couple of brownstone buildings, are located at the intersection.

Members of the local 13th Precinct knew of the man and said he has claimed to be homeless in the past, cops said. 

A nearby building super said he arrived at work at 5:40 a.m. and spotted the body about 5 or 6 feet away – with cops and firefighters gathered on the closed off street. 

“I saw him. He was in the street,” the super said. “He was on his back. I know because his hands were bent at the elbows and his fingers were stiff. His feet were stretched out.

“The whole body was burned. Everything was black. I couldn’t tell if he was white, black, Hispanic.”

The super, who said he’s spent 20 years on the block, said that homeless people are known to sleep in front of the church. 

“They fight, they do drugs there. It could be one of them,” he said. “I feel bad. No matter if he was homeless, it doesn’t matter. He’s still a human being.”