Video from the Museum of Modern Art shows the moment a man leaped over a reception desk and stabbed two employees as they tried to flee on Saturday.
The video released by New York City police shows a man police identified as Gary Cabana, 60, entering the museum lobby through a revolving door then climbing on to the desk and jumping over it as a man carrying what appears to be a walkie-talkie tries in vain to stop him.
Police were still searching for Mr Cabana as of Sunday morning.
The man, wearing a black wool hat and a surgical mask, approaches three employees who are trapped in the small space and stabs one of them — a young woman who is able to run away seconds later but not before she is stabbed again, in the back.
The attacker then stabs the second employee as the man with the walkie-talkie hurls a notebook at him. That distracts the attacker long enough for the second victim to flee.
A third employee gets up from the ground after the attacker runs away.
Authorities said Saturday that the two museum employees — a man and a woman, both aged 24 — were in stable conditions with non-life-threatening injuries.
Police said Mr Cabana was denied entry on Saturday for previous incidents of disorderly conduct.
John Miller, NYPD deputy commissioner of intelligence and counter-terrorism, said Mr Cabana's membership had been revoked for two incidents of disorderly behaviour at the museum in recent days.
A letter informing him of his expired membership was sent out on Friday, but he went to the museum on Saturday saying he intended to see a film there, police said.
He then became upset and stabbed the museum employees in the back, collarbone and the back of neck, Mr Miller said. They were taken to hospital within minutes.
Mr Miller said on Saturday that the video showed which way the suspect went after leaving the museum. Police shared photos of Mr Cabana late on Saturday night, asking for the public’s help finding him.
The department has no record of a previous arrest for the man.
The midtown Manhattan museum was emptied of patrons on Saturday afternoon.
Visitor Yuichi Shimada tweeted that he was on the second floor when a couple came running towards him, and he heard security guards’ radios throughout the museum.
“It was chaotic, partly because it was snowing, with a group of young women in a panic and crying,” Mr Shimada said. “Not being good with claustrophobia myself, I headed for the exit early.”
He was diverted to the side on his way out as a stretcher was hurriedly brought in.
Police vehicles and ambulances, with emergency lights flashing, gathered outside the museum as dozens of patrons hurried away.
Mayor Eric Adams tweeted on Saturday evening that he had been briefed on the attack and said the victims’ injuries were not life-threatening.
“We’re grateful for the quick work of our first responders,” said Mr Adams, a former NYPD captain.
The museum, founded in 1929, is one of New York City’s top tourist attractions, and drew more than 700,000 visitors in 2020.
The Associated Press contributed to this report.