'So terrifying' - New Yorkers describe scrambling for cover in rush-hour skyscraper shooting

Workers in New York City have described scrambling out of office blocks, as panic engulfed part of downtown Manhattan when a gunman opened fire and killed four people on Monday.

People poured out of skyscrapers and onto the busy streets of the US city, some with their hands in the air, while others sheltered in buildings nearby.

The violence unfolded in the early evening inside the 44-storey building at 345 Park Ave, home to the National Football League (NFL) office, as well as financial giants Blackstone and KPMG.

Nekeisha Lewis said she was eating dinner with friends on the plaza when she heard gunfire.

"I looked up and I saw the first wall of the first floor shatter," she told NBC News.

"I realised 'oh my God, this is a shootout'," she said. "It felt like you were in a warzone almost."

Ms Lewis then said she saw an injured man run out of the building.

"By the time he got to us he said: 'Help, help, I've been shot.'"

Ms Lewis said she and her partner helped the man get away from the building before police took over.

"It's been literally the most scary situation I've ever been in," she said.

Local TV footage showed lines of people evacuating the office building with their hands above their heads in the hours after the killings.

Another witness, Jessica Chen, told ABC News she was watching a presentation with dozens of other people on the second floor when she "heard multiple shots go off in quick succession from the first floor".

She and others ran into a conference room and barricaded tables against the door.

"We were honestly really, really scared," she said, adding that she texted her parents to tell them that she loved them.

Some workers from another nearby building were picking up food from a local outlet when they heard a loud noise and saw people running, AP reported.

"It was like a crowd panic," said Anna Smith, explaining that she and others had returned to their place of work to find shelter. She said they were told they could leave after about two hours.

A BBC journalist at the scene reported seeing scores of police vehicles and at least one person with a bloodied chest being taken away on a stretcher.

Bystanders reported hearing what sounded like gunshots and police told those in the area to shelter in nearby buildings.

Mama Bouhenni, working at the nearby Sip & Scoop coffee shop as the incident unfolded, told the BBC she saw dozens of people from surrounding buildings being evacuated.

They held their hands above their heads, she said.

Ms Bouhenni said she recognised many of them as her shop's customers. "This is so terrifying for them, I hope they can go home safe."

With reporting by Indrani Basu