A homeless man known for “violent” behavior and drug use at a local shelter was arrested for stabbing two people in separate, unprovoked attacks in Hell’s Kitchen, cops and sources said Thursday.

Nickolas O’Keefe, 33, was linked to the two Wednesday evening stabbings, including one targeting a 27-year-old ER nurse on his way to meet a friend for dinner, police and the victim said.

“I saw this guy walking towards me, and I didn’t think anything of it, I was just walking, and I saw him reach to his back and as soon as we passed each other he just turned around and stabbed me in the back,” said the victim Christopher, who asked that his last name not be used.

“I was so in shock, like did I really just get stabbed in the middle of the day?” Christopher told The Post, saying the weapon was a steak knife. “My friend was a block away from where I was meeting, and I just ran to her like I think I just got stabbed, can you look at my back? And she’s like yeah you’re bleeding.”

Christopher stumbled away, confused after the random attack, on West 50th Street near Tenth Avenue at around 7:20 p.m. – while it was still light out.

He rushed to the emergency room at Mount Sinai West, and another woman attacked by the same person about soon came in for treatment. The other victim, 27, was stabbed in the chest about 30 minutes later on West 47th Street near Tenth Avenue, cops said.

“He said nothing to me, nothing to the other girl, and nothing after. He didn’t take anything,” Christopher said of his attacker. “He just did it and kept walking. And that made it also feel like, did this really happen? It’s just so weird. Like it happened so fast, but like in slow motion, I see him turning to stab me, and I’m like this man is stabbing me right now on the street.”

Both victims described their deranged attacker as a man who appeared to be in his 30s, with a light complexion, wearing a yellow shirt with khaki pants. 

Police searched the area and stopped O’Keefe at the corner of West 46th Street and 9th Avenue, cops said. The male victim confirmed that O’Keefe was in fact his attacker, cops said. 

O’Keefe was charged with two counts of assault and criminal possession of a weapon in the incidents.

O’Keefe’s address is listed as a nearby shelter on West 48th Street near 10th Avenue. Police believe he is homeless, sources said.

He had one prior arrest on his record for criminal sale of marijuana in 1989, according to sources.

He allegedly bought crystal meth on the morning of the attack, Charles Hagler told The Post.

“For the last two three days, sometimes he come here, sometimes he don’t. He be doing drugs, I know that,” Hagler said.

“Yesterday he was quiet, but I knew something was going on because for the last two, three days he keeps wearing the same clothes over and over. Striped shirt, khakis,” Hagler went on. “He had that on for two-four days, so I know he ain’t functioning right. He been up for four days straight. I know this because the staff, they be talking about it.”

“He’s been real quiet, but violent [two days ago] he threw a mattress into the stairwell and they had to go and get it out the stairs.”

O’Keefe, who has stayed at the facility for about four years, gets “aggressive” when he drinks, Hagler said. In April, he went missing for about a week, Hagler added.

“I seen him with a knife, in July, a little pocket knife,” Hagler, 54, said. “Once I see him with a steak knife three weeks ago.”

 “He basically a loner, he don’t talk to nobody, but he be yelling and screaming in his room sometimes. He slams people’s doors,” the resident said. “One time he threw all the chairs down the stairwell. When he drinks he returns into a whole different person.”

Christopher said his harrowing ordeal has left him feeling “unsafe” living in the city.

“Like working in the ER I see how bad it is, how bad mental health is, how bad crime is, and there is nothing being done about it, it feels like,” Christopher said.

“I was talking to my boyfriend, like I don’t feel safe living here. It’s really discomforting not to feel safe in your home,” he said. “I don’t want to leave the Upper West Side. I work down in Soho, I have to take the subway, through Hell’s Kitchen, through Times Square – alone — and I don’t even want to do that alone right now.”

Mayor Eric Adams has to “do something” about the mental health and homeless problems that are “only getting worse and getting so out of hand that it’s affecting people in the middle of the day,” he said.

“We all hear about this happening to people, and now my friends are like, ‘Now this is actually happening to someone we know,’” he said. “’It’s just a matter of time before I’m in that situation,’ my friends are telling me.