The street sweeper arrived at 12th and Arch shortly after dawn.

With a broom and a wheeled dumpster, he swept around the sleeping forms on the sidewalk under the arches of the Convention Center. As commuters walked past and dozens on the sidewalk stirred awake, the street sweeper collected bottles and plastic wrappers and half-eaten food - all the detritus of a night on the streets.

"Clean this dump up," muttered Paul Bunn, folding up his cardboard sleeping mat.

There were 55 souls like Bunn waking up on the sidewalk outside the Convention Center one recent morning. They have been there for months, advocates and city officials say, ever since construction on the Benjamin Franklin Parkway and in LOVE Park forced many of the city's homeless to find new places to sleep. For them, the Convention Center underpasses - dry, sheltered from the elements, and well-lit - are a natural choice.

With a community of homeless people sleeping in front of one of the city's main attractions, a problem that has long stymied the city is more prominent than ever. Center City's boom, and its attraction of major events like next month's Democratic National Convention, has thrown the human suffering on its streets into sharp relief.

"Philadelphia is a city that cares - and if no one cared, one would be upset," said Sister Mary Scullion, who runs the homeless outreach organization Project HOME and has been fielding calls for months about the shift of the homeless population from the outskirts of Center City to its heart. "This tension, hopefully, will produce results."

Convention Center officials say that last year, the population sleeping in the tunnels skyrocketed from a scattered few to clusters of people sleeping under blankets, in tents, in boxes for nights on end.

The center's director, John McNichol, met with Philadelphia police and various city agencies shortly afterward.

"I don't feel like any of us believe the solution is pushing people onto someone else's doorstep," McNichol said.

Paul Levy, who heads the Center City District, a business owners' organization, said it is hard to pin the increased population under the Convention Center on one cause. About 700 people are sleeping on the streets citywide - hundreds in Center City, and hundreds more in the open-air drug markets of Kensington.

Advocates say a dearth of federal funding, the aftereffects of the recession, and an opiate crisis fueled by prescription drugs and inexpensive, potent heroin contribute to a 2 percent uptick in the homeless population this year.

Whatever the cause, Levy said, the more visible homeless community raises crucial questions about the way the city deals with the problem: "Does the city have all the right options for people on the street?"

The Office of Supportive Housing, under a new mayor, is readying its own plan to combat homelessness, including a new policy of sending teams of street outreach workers to homeless "hot spot zones" in Center City, including the Convention Center.

Workers try to persuade people to come inside, but even if everyone on the street elected to, there would be far too few beds.

"I think the homeless situation is distressing to everyone: the city, the hospitality community, the residents," said Liz Hersh, director of the Office of Supportive Housing. "It's not the way it should be."

At the hotels on Race Street that host convention crowds, employees said customers often mention the slumbering homeless.

"I think it's kind of embarrassing for the city and the Convention Center, when they're having conventions over there and they're lying there sleeping," said Crystal Bogan, who manages the front office at the Days Inn at 12th and Race Streets.

McNichol says the Convention Center works to make sure its sidewalks are cleaned each morning. A crew of street sweepers picks up trash and hose down the sidewalks. The Sixth Police District has a substation under the 13th Street arch. Convention Center workers ask those sleeping in the tunnels to move when shuttle buses pull up to the center in the early mornings, he said, and position security guards at the entrances.

"People are coming here from all parts of the country," he said, and some get alarmed simply because they're unfamiliar with urban settings and "may have never seen homeless people.

"But they're human beings and they have rights," he added. "You have to respect those rights, and also make the customers feel comfortable."

Philadelphia Police Chief Inspector Dennis Wilson said the department regularly fields complaints from neighbors and businesses about people sleeping on the streets.

"It's a fine line we try to balance," he said. Police are able to cite people for blocking the right of way on sidewalks, but take a homeless outreach worker along when they do so, Wilson said.

"We would like nothing more than to ride every homeless person to a shelter," he said.

Homeless advocates have long argued for the right to sleep outside, and won several court cases on the issue during previous city administrations.

"It is not a crime, nor should it be a crime," said civil rights lawyer Paul Messing. "What's criminal is that we, as a society, are not devoting the necessary resources to the problem."

Though no cure on its own, Hersh hopes the city's new, more-targeted outreach can persuade people hesitant to come inside to do just that.

"Repeated contacts with team members is what gets them to go in for services," Hersh said. "We're really trying to cultivate relationships."

On a cool night earlier this month, Project HOME outreach workers in bright orange shirts crossed 12th Street and spoke to a woman with a heap of bags next to her. She scratched at a badly swollen ankle as a worker tried to persuade her to go to a hospital for treatment - and then, when she refused, offered her Project HOME's hotline number. Call the dispatcher there any time, the worker said, and someone would come to help.

The woman paused. "Dispatch," she said, looking alarmed. "Is that the police?"

Late on another night, as businesses closed and tourists walked through the underpass to the Race Street hotels, a 57-year-old man named Charles and his girlfriend trekked up the street with backpacks and blankets in tow.

They said they had been homeless for about five years. They'd picked the Convention Center, they said, because it was warm and dry, and because shelters have strict rules and bedbugs. They, like so many, had waved off the outreach workers.

Across the street, Martin Polisano, 61, had laid down next to a row of other men. He has been sleeping on the streets on and off for years, he said, battling heroin addiction.

"You can't get any lower than this," he said, "other than death."

He picked at a plate of barbecued chicken and rice, courtesy of the Community Outreach School Project, a local nonprofit that feeds the homeless. The group used to drive to the Parkway, and then LOVE Park, but people stopped sleeping there. A tip from a beat cop had directed the group and its barbecue to the Convention Center.

Scullion said the Convention Center is simply the latest spot in Philadelphia - and one of the most visible places yet - to encounter a problem that the city has worked to solve for years.

"What was once LOVE Park's problem is now the Convention Center's problem," she said.

But there are so many more that remain in the shadows, Scullion said, out of sight of the commuters and the tourists and the condominium owners.

On a crowded night at the Convention Center, sixty people take shelter in the tunnels.

In Kensington, as many as 300 sleep on the streets each night.