Authorities and service providers are struggling to find long-term solutions to Melbourne's homelessness crisis, with police saying they cannot move people on if they are not breaking the law.

The homeless population in the city has visibly increased in the past 12 months, with small camps popping up around the grid.

Traders and the public have made a number of complaints about one large makeshift camp outside Flinders Street Station, where council officers recently counted 19 rough sleepers.

There have also been media reports of drug taking, often in broad daylight and busy peak periods.

The City of Melbourne, Victoria Police and support services have been working to try and find solutions to the issue without luck.

Superintendent David Clayton from Victoria Police said despite the concerns from the community, officers could not make people move.

"I understand their frustration, but currently it's no offence to be homeless and sit or sleep on the street," he said.

"It doesn't address the underlying cause of homelessness. It doesn't solve the problem of people on the street, it moves them simply to another location."

No-one has been able to solve homelessness: Mayor

Rough sleepers said they chose Flinders St because it was safer. ( Flickr: Michael Coglan )

Mayor Robert Doyle said outreach workers were trying to help homeless people on the streets, rather than waiting for them to turn up at an agency.

"In the end the only way to solve the problem is to solve rough sleeping and I don't know of anybody in Australia who's done a terrific job of that," he said.

Last week police moved in and removed some of the camps dotted around the city, including some of those set up at Flinders St.

Under law, police are able to remove makeshift structures and do so on a weekly basis, Superintendent Clayton said.

He said housing support was being offered to those living on the street, but some were not taking it up.

"We work with the service agencies to link them to housing, [but] if people don't take the housing option it's difficult to move them on.

Homeless choosing Flinders St because it is 'safe'

One of the people living at Flinders St, Sharon, told ABC Radio Melbourne she was there because she felt safe.

"The reason I sleep here is because I know there are cameras up the road, I know I'm safe every night," she said.

"There are coppers — protective service officers — that walk past everyday, every couple of hours or so to check on us to make sure we're alright.

"People should know that we're not all on drugs. Yes, some of us smoke a pipe every now and then because we're stressed."

Superintendent Clayton said some of the people seen using drugs, or smoking bongs, were actually using synthetic drugs.

He said current laws had not yet been updated to classify those substances as illegal.

"When we are aware that people are using drugs of dependence, we take appropriate action to charge them and put them before the courts," he said.

"We have no power to move people if they're not committing offences."