ZURICH (AFP) - As the Swiss city of Zurich opens the country's first sex drive-in to better regulate prostitution and move the sex trade outside the city centre, residents, politicians and sex workers remain divided over the scheme.

The nine so-called "sex boxes" will be available to prostitutes and their clients from Monday onwards, in a former industrial zone in the west of the city.

Inspired by a similar initiative in Germany, the Zurich authorities want to alter the image of the city's Sihlquai district, where sex workers openly ply their trade each night, to the dismay of residents.

"Prostitution is a business basically. We cannot prohibit it, so we want to control it in favour of the sex workers and the population," said Mr Michael Herzig, director of social services for sex workers in the city.

"Because if we do not control it, organised crime is taking over, and the pimps are taking over," he added.

When AFP visited Sihlquai on Friday, half-naked women were standing on street corners in little more than their underwear, and sometimes even less, with one woman dancing provocatively to attract passing cars.

A tall blonde sex worker in bright red underwear organised a group of women and offered them up to potential clients, who pulled up every five minutes to inspect the lineup. It was not yet 9pm.

The local authorities recognise that they have no guarantee that the new site will be successful, but have worked hard to convince prostitutes to come and inspect the premises.

The sex boxes are hard to find, behind a high fence with just a small sign displaying opening hours and a red umbrella icon to designate a regulated sex work area.

There are clearly defined rules. Clients must be older than 18, one to a car, and condoms must be disposed of immediately after use in the bins provided.

Behind the fence, a round track where clients make a choice and the women negotiate a price is flanked by the sex boxes - wooden frames that look like car ports where they can park and complete the transaction.

"Here, they remain onsite and can deal with customers quickly," said Ms Ursula Kocher, director of Flora Dora, a support network for prostitutes.

In town, clients regularly take prostitutes to a nearby forest or outside the city, where the sex workers regularly find themselves in dangerous situations, she said.

In the sex drive-in, prostitutes operated in a safe environment, Ms Kocher said, pointing out that in an emergency each sex box is equipped with an alarm button to alert a permanent security presence.

"The problem with the Sihlquai is that there are quite a lot of women, and it's a normal street in the middle of Zurich and all the neighbours and all these people living there had troubles because of the sex workers," she explained.

Violence against sex workers often follows from misunderstandings between clients and prostitutes, as the sex trade in Zurich is dominated by Hungarian Roma who speak only rudimentary German, she said.

In an article published on Friday in the Swiss tabloid 20minuten, several prostitutes expressed reservations over the sex boxes, saying that this tightly controlled environment might intimidate their customers.

If some say they are ready to give it a try, others do not hide that they will simply take their business to the northwest of Zurich, once prostitution is no longer authorised in the city centre once the sex drive-in opens on Monday evening.

The proposed sex drive-in was approved by the people of Zurich in a March 2012 referendum, with 52.6 per cent voting in favour.

And the idea has a broad consensus among political parties, with only the populist Swiss People's Party (SVP) opposing the project.

"It will not work, either because the clients will not come or because the site will not be used by prostitutes," said Mr Sven Oliver Dogwiler, a local SVP politician.

"It puts them in a cleaner space but one that is subsidised by taxes," he told AFP on Saturday.

The work cost 2.1 million Swiss francs (S$2.94 million), and operating costs will be approximately 700,000 Swiss francs a year.

Zurich residents came to inspect how their money was spent at an "open doors event" Saturday.

A resident who gave her name only as Claudia, 30, lives on the other side of Zurich and was visiting the sex box site out of curiosity. "I'm ambivalent. Somehow I think it's good," she said.

"The security, the condoms, the good hygiene. But the business itself should be questioned. Many women don't do this freely."

Others were unimpressed. A woman who gave her name only as Trudi, 74, whose daughter worked in security at the site, told AFP: "The people are paying for this... It's their business, nor ours. We shouldn't be using taxes for this... I don't understand."