The ice was falling on West Street, which was closed in both directions along with southbound lanes from Canal Street to the Battery Park underpass, while northbound lanes were shut from the underpass to Murray Street.
All streets were reopened by 3:30 p.m.
The ice, chunks as big as a few feet, was falling from 1 World Trade Center and shattering on the ground.
The street closures caused major delays in Lower Manhattan and at the Brooklyn Battery Tunnel, where traffic was diverted.
"The snow starts to melt and the liquid drips off and makes bigger and bigger icicles, or chunks of ice that break off skyscrapers," said Joey Picca, a meteorologist at the National Weather Service in New York, which has had 48.5 inches of snow since the start of the year, and several cycles of freeze and thaw.
"Be very, very aware of your surroundings," he said. "If you see ice hanging from a building, find another route. Don't walk under hanging ice."
Some architects say newer, energy-efficient high-rises may actually be making the problem worse.
"They keep more heat inside, which means the outside is getting colder and that allows more snow and ice to form," said engineer Roman Stangl, founder of the consulting firm Northern Microclimate in Cambridge, Ontario.
Stangl helps developers opt for shapes, slope angles and even colors - darker colors absorb more melting sunrays - to diminish ice formation. High-tech materials can be also be used, such as at Tokyo's Skytree observation tower, where heaters were embedded in the glass to melt the ice.
Such options are not always possible in older cities with balconies, awnings and stone details.
Barry Negron said he saw ice hanging perilously off a four-story building near Rockefeller Center last month and was trying to warn other pedestrians when he was hit in the face with a sharp, football-size chunk. Cuts across his nose and cheek required 80 stitches.
"I panicked because I saw blood on my hands, and more coming down," said the 27-year-old salesman. As he lay on the pavement, "I heard two young ladies yelling, 'Oh, my God, oh my God, help! There's a lot of blood!'"
Since then, he's nervous when he walks around the city and has seen other near-hits. "I look at my scars, and I say, 'Why did this have to happen to me?'"
Exactly how many pedestrians are hit by falling ice is not clear, but dozens of serious injuries are reported annually.
(The Associated Press contributed to this report)
