The first customers arrived at Switzerland’s new sex drive-in last night to be greeted by a waiting pack of journalists rather than prostitutes.

The first man to arrive on opening night took one lap of the facility before making a hasty exit.

The second car, a family vehicle driven by a man in sunglasses, broke down and needed jump starting in front of a host of photographers, sniggering into their cameras.

Swiss authorities had said they expected a modest start to the country's first "sex boxes", a row of drive-in wooden garages on a looping track where clients in cars can visit prostitutes, shielded from prying eyes and security cameras.

With an estimated annual turnover of around 3.5 billion Swiss francs (€2.9 billion), prostitution has been legal in Switzerland since 1942, with sex workers in Zurich required to have a special permit, health insurance and pay tax.

The number of prostitutes in the country has risen sharply over the last decade, due to the decriminalisation of procuring and passive solicitation of sex alongside agreements between Switzerland and the European Union on free movement of people.

The sex boxes, which echo similar drive-in systems in the Netherlands and Germany, are being touted as a way to get large numbers of prostitutes and their clients off Switzerland's otherwise pristine streets.

Complete with panic buttons in each shed, showers, a laundry room and on-site health workers, supporters say the system offers relative security to sex workers and privacy to their clients, while reducing the disturbance to locals.

"The existing strips were simply too strained," said Ursula Kocher at Zurich's welfare department.

"The conditions for the women were completely unhygienic and dangerous, they had to work in woods or secluded car parks," Ms Kocher said, standing in front of the boxes.

Only four prostitutes were on site at the start of the evening, but Ms Kocher said she was sure more women would come to the compound, where they would have access to contraceptives, counselling and sexual health checks.

Between 7pm and 5am, men can cruise along the track and choose a prostitute from wooden shelters before parking in one of the nine drive-in boxes.

Though clients must arrive alone in a car, they also have the option of parking and visiting two smaller boxes or one of four camper vans on foot.

Prostitutes at the facility declined to talk to journalists or allow them to take their pictures.

Some critics have voiced concern that the novel fascination with the sex boxes, which have cost taxpayers more than €1.6 million to construct, is a distraction from more serious issues about exploitation and human trafficking.

"It would be more revealing to ask: what sort of men buy sexual services of young women on the street?" said Andrea Gisler, president of Zurich's Frauenzentrale women's group, adding the boxes only relocated red light activities to the outskirts of the city.

"The prostitutes and their protection has never come into it," Ms Gisler said.

The conditions for sex workers may be better in countries where prostitution is legal, but a global study showed this year that they also report higher influxes of human trafficking.

One author of the study, Eric Neumayer at the London School of Economics, said the new system in Zurich could aid monitoring of human trafficking.

"If it's a very controlled environment, it should be easier to do checks on where the women come from, if they are there against their will," Mr Neumayer said.