Residents of US cities facing one of the most brutal winters on record have been dealing with something far more dangerous than snow: ice falling from skyscrapers.
Several streets around New York's 1 World Trade Centre, the nation's tallest building, were closed on Wednesday morning when wind-blown shards of dagger-shaped ice hit the pavement near the 541-metre building.
The streets reopened by mid-afternoon.
Around the nation, pavements around high-rises in cities have been cordoned off because of falling icicles and rock-hard chunks of frozen snow. Experts warn it could get worse over the next few days as a thaw sets in over much of the United States.
"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. The city has had 123cm of snow already this year.
Some architects say newer, energy-efficient high-rises may 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 choose shapes, slope angles and even colours to diminish ice formation. Hi-tech materials also can be used, such as at Tokyo's Skytree observation tower, where heaters were embedded in glass to melt the ice.
Such options are not always possible in older cities with balconies, awnings and stone details.
Barry Negron, 27, said he saw ice hanging perilously off a four-storey building near Rockefeller Centre 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," he said.
Exactly how many pedestrians are hit by falling ice is not clear, but dozens of serious injuries are reported annually.
It is a perennial problem in the architecturally stunning St Petersburg, Russia, where dozens reportedly are injured or killed every year.
Seven people were injured in 2011 near Dallas when huge sheets of ice slid off the roof of Cowboys Stadium. Another 15 people were injured in 2010 by a shower of ice from the 37-storey Sony Building on New York's Madison Avenue.
Outside Chicago's 100-storey John Hancock Centre last month, people scrambled with backpacks and purses over their heads to avoid falling ice.
On Tuesday, signs warning pedestrians of falling ice stood outside nearly every skyscraper and other tall buildings in the city centre as temperatures pushed above freezing for the first time in weeks.
"This happens all over the country, all over the world, in cold climates," said architect Chris Benedict, who accounts for ice build-up in designing new structures.