So many rats regularly lurk on a sidewalk in Brooklyn that it is the humans who avoid the rats, not the other way around.

Not even cars are safe: rats have chewed clean through engine wires.

A Manhattan avenue lined with trendy restaurants has become a destination for foodies — and rats who help themselves to their leftovers.

Tenants at a public housing complex in the South Bronx worry about tripping over rats that routinely run over their feet.

New York has always been forced to co-exist with the four-legged vermin, but the infestation has expanded exponentially in recent years, spreading to just about every corner of the city.

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“I’m a former Marine so I’m not going to be squeamish, but this is bad,” said Pablo Herrera, a 58-year-old mechanic who has counted up to 30 rats while walking on his block in Prospect Heights, just around the corner from the stately Brooklyn Museum.

Rat sightings reported to the city’s 311 hotline have soared nearly 38 percent, to 17,353 last year from 12,617 in 2014, according to an analysis of city data by OpenTheBooks.com, a nonprofit watchdog group, and The New York Times.

In the same period, the number of times that city health inspections found active signs of rats nearly doubled.

Mayor Bill de Blasio, like mayors before him, has declared war on rats, but so far the city is still losing.

“There is no doubt that rats have a major impact on New Yorkers’ quality of life and this administration takes seriously our responsibility to control and mitigate their population,” said Laura Anglin, deputy mayor of operations.

“No New Yorker likes having rats in their community and we are committed to continuing the work of controlling rats in all of our neighbourhoods.”

One key reason rats seem to be everywhere? Gentrification.

The city’s construction boom is digging up burrows, forcing more rats out into the open, scientists and pest control experts say.

Milder winters — the result of climate change — make it easier for rats to survive and reproduce. And New York’s growing population and thriving tourism has brought more trash for rats to feed on.

But the onslaught of rats extends beyond New York: Cities such as Philadelphia, Chicago and Los Angeles are also confronting outbreaks.

“Everywhere I go, rat populations are up,” said Robert Corrigan, a research scientist in New York who estimates that their numbers may have increased by as much as 15% to 25% in some cities.

The rodents are not only a nuisance and a blight on the quality of life, but also a health risk. A bacterial infection spread by rat urine, leptospirosis, killed a Bronx resident in 2017.

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Chicago — crowned the nation’s rat capital in one study — has more than doubled its work crews dedicated to rats, who set out poison and fill in burrows in parks, alleys and back yards.

It also passed ordinances requiring developers and contractors to have a rat-control plan before demolishing buildings or breaking ground on new projects.

Washington, where rat complaints have nearly tripled to roughly 6,000 last year from 2,400 in 2014, is testing a rat-sterilisation program tried elsewhere that uses liquid contraceptives as bait.

And Seattle is planning to train neighbourhood property owners and managers on how to stem infestations.

“We respond where we can, but management of rats, not elimination of them, is our practical goal,” said Hilary Karasz, a county health official.

In New York, rats once scurried in the shadows but now they frolic brazenly in broad daylight.

One even became a social media star: pizza rat. Parents at an Upper West Side playground said rats jumped into the sandbox where their children played, though the vermin have been cleared for now.

De Blasio, calling for “more rat corpses,” unveiled a $32m (£25m) assault on rats in 2017, which included increased litter basket pickups, the deployment of solar-powered, trash compacting bins and rat-resistant steel cans.

The city has also used dry ice to smother rats where they live.

But after dropping last year, rat sightings are again on the upswing. The top spot for rat sighting complaints has been the Upper West Side, where residents are known for speaking up, followed by four Brooklyn neighbourhoods: Prospect Heights, Bedford-Stuyvesant, Bushwick and Ocean Hill.

Jason Munshi-South, a biology professor at Fordham University who has led “rat safaris” to observe the vermin in Columbus Park in Chinatown, said that while New York is doing more than other cities, it will never be able to entirely eradicate rats.

A major contributing factor is how the city collects trash: bags are left outside on the curb for hours before pickup the next morning. “It’s just an all-night buffet for the rats,” he said.

On Ninth Avenue in Midtown Manhattan, rats chow down on trash bags piled outside restaurants and bars.

Bin in New York's Chinatown warns 'a little litter can lead to big problems' (Stephen Speranza/The New York Times)

Steve Belida, the chairman of a local block association, said he used to get the occasional rat complaint. Now he gets a steady stream.

Michael Deutsch, an entomologist with Arrow Exterminating on Long Island, said there is no “magic bullet” to reducing rats.

“You can’t just go in and order an airstrike — and then leave,” he said. “Rat populations can rebound unless you are always pressing them.”

Even buildings that never have had a rat problem are now being inundated by those rodents.

Larry Jayson said he recently saw a rat jump out of a trash bin in an apartment building that is next to a new tower under construction in Flatbush, Brooklyn. It was the largest rat he had ever seen.

“We’ve seen rats the size of Cleveland,” said Jayson, the executive director of Housing and Family Services of Greater New York, a non-profit organisation.

“You’re unearthing and unleashing hell on those poor people who live next door.”

Under the city’s building code, developers are required to hire a licensed exterminator for any site where a building is being demolished. But there is no similar rule for new developments.

Simon H Williams, a researcher at Columbia University’s Mailman School of Public Health, likened the impact of the construction on rats to “stepping on an ants' nest”.

In Prospect Heights, rats have made themselves at home on a block of Lincoln Place that has attracted young families and middle-class professionals.

A rundown building on the corner is being renovated while several new buildings are going up nearby, contributing to the local rat population.

On a recent night, black trash bags piled along a stretch of sidewalk known as “rat alley” seemed to crinkle on their own as rats squirmed inside. High-pitched squeaks filled the air. “It’s not the night before Christmas,” said Mr Herrera, who lives next door.

Mr Herrera has found gnawed chicken bones and rat droppings underneath his car hood. He spent $150 (£118) to replace chewed-up ignition wires.

Walking down the street has become a source of anxiety for his nine-year-old daughter, Isabella Henry.

Despite numerous complaints to city officials — including dozens of calls to 311 — the rats keep turning up.

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Residents say they feast on garbage left outside the apartment building under renovation on the corner, which has failed 10 city health inspections since last year, according to records.

Getz Obstfeld, a co-owner of FSG Realty, which manages and partly owns the building, said that they have targeted rat holes, added more trash cans and removed construction debris.

Still, the rats keep coming.

“They love it over here, it’s up and coming,” said Russell Coit, 66, a retired maintenance supervisor who lives on the block. “They would like to invest in something over here, too.”