NEW YORK - From an office by the Brooklyn Bridge, a specialized team of investigators tackles a fast-growing concern in the nation's biggest city: apartments being rented like hotel rooms.

Building and fire inspectors, police, lawyers, city tax specialists and others combine door-knocking, digital sleuthing and even video surveillance in an uncommon approach to an issue bubbling up around the country.

New York's investigators have cited over 7,000 fire and building code violations, shut down over 200 short-term apartments and sued several operators - ending an additional 250 short-term rentals - over the last nine years, according to the Mayor's Office of Special Enforcement. With Airbnb and other websites sparking a short-term rental boom, some lawmakers now want to triple the illegal-hotel investigation staff and have it go beyond answering complaints to scour the web for suspect listings.

"The problem has skyrocketed in the past few years," and enforcement must keep pace, says City Council Housing and Buildings Committee Chairman Jumaane Williams.

But some proprietors have called the city's tactics heavy-handed. Airbnb says New York unfairly lumps occasional users in with hotel-scale operators, although officials say enforcement focuses on big players.

"It can get overzealous," says Airbnb public policy head David Hantman, who wants New York laws changed to exempt people renting out their own homes and "target the truly bad actors."

It's largely illegal in New York to rent entire apartments for under 30 days, though it can be OK to rent out spare rooms if a resident also stays home.

Yet vacation rental sites boast many apartments. The city fielded 1,150 illegal-hotel complaints last year, up 62 percent from 2013.

Hosts say "home sharing" helps them pay bills and makes traveling funkier and cheaper. But city officials note that guests generally don't get fire sprinklers and other safety features required in hotels, and residents contend with rotating casts of strangers.

"You get on the elevator, and you don't even know who's going to get on," says Audrey Smaltz, a fashion-industry entrepreneur whose Manhattan apartment building has been used as a $500-a-night hotel, according to a city lawsuit. "I don't feel safe."

Countless travelers have learned the front-door entry code, and a stranger wandered onto the roof and stared at Smaltz through her penthouse terrace window one night last fall, she said.

There are no short-term rentals in the building now, the owner said in court papers.

Many cities are addressing, and sometimes allowing, short-term vacation rentals. San Francisco is now crafting rules permitting some home-as-hotel stays and determining enforcement procedures. In Chicago, a business and consumer department handles unlicensed vacation rental complaints and can issue fines.

New York, meanwhile, uses its multi-agency Mayor's Office for Special Enforcement.

Investigations generally start with a police officer, fire inspector and building inspector knocking on doors and asking denizens whether they live there, acting director Elan Parra says. When investigators find a paying visitor, they'll request booking details.

That can lead to violation notices, fines, follow-up inspections and evacuations, if inspectors declare a serious safety threat.

The consequences might not end there. Using software to cross-reference information, investigators look for patterns in complaints, listings, lessees, building owners, managers, companies or other factors that might point to a multiple-apartment operation and warrant not just administrative fines but a lawsuit for damages. Occasionally, investigators will stake out a building with video cameras, Parra said.

"We focus on the places where people are complaining, where there are clearly presented concerns and issues. ... We want to make sure that we're allocating our resources to getting and eradicating the absolute worst operators" and safety risks, Parra said. This month, his office shut down three Brooklyn dwellings it said were bunk-bed-stuffed, fire-hazard hostels.

Meanwhile, City Councilwoman Helen Rosenthal and several colleagues called for expanding the staff from 11 to about 36. Councilman Ben Kallos wants the city to post publicly how illegal-hotel complaints are resolved.