In a sunny nursery in Yokohama with shiny wooden floors and freshly painted walls, a group of limber pre-schoolers are doing gymnastics. They will follow this with music practice on the pianica – the portable keyboard beloved of Japanese kindergartens. Smells waft from the kitchen where home-cooked lunches are prepared. Outside there is a grassy area for the children to play on. So far, so idyllic. Yet Byobugaura Harukaze Nursery, which opened last April, is unusual. It is built under a highway. The road above is so well insulated that, apart from the babble of 52 boisterous children, the nursery is surprisingly peaceful. “Some parents had questions,” says the principal, Takeshi Takahashi, “but once they came here and saw it for themselves they felt reassured.”

Byobugaura is one of dozens of nurseries that have been built in Yokohama as it has undergone an extraordinary shift from having the longest nursery waiting list in Japan in 2010 to no waiting list at all. In record time the city increased the number of certified nurseries by 160 and added an extra 12,000 places. Prime Minister Shinzo Abe promptly called for the “Yokohama Method” to be replicated up and down the country.

The woman responsible for Yokohama’s rapid turnaround is the city mayor Fumiko Hayashi. A former ceo of Daiei (one of the biggest supermarket chains in Japan), she is a warm but formidable presence who understands the challenges facing working mothers. “I’ve experienced first-hand the hardships of women working in male-oriented businesses,” she says. “So this was my personal mission.”

When Hayashi was elected in 2009 she got straight to work on what she saw as the biggest obstacle to getting mothers back to work – the shortage of childcare. She pledged to eliminate nursery waiting lists and she set about reinventing the childcare set-up in Japan’s second-largest city.

For an industrialised country with one of the best-educated populations in the world, Japan has some worrying statistics when it comes to women’s position in the workplace. In the World Economic Forum’s 2013 Global Gender Gap Report, Japan languishes at 105, sandwiched between Cambodia and Nigeria. Fewer than 5 per cent of listed company board members and 8 per cent of Japan’s lawmakers are women. Roughly two thirds of women don’t go back to work after childbirth.

“[Japanese] women’s participation in the workforce drops in their thirties,” says Hayashi. “And in Yokohama more than most.” Returning to work after childbirth is particularly difficult. “Women often have to quit. Either they aren’t being promoted or they can’t find nursery places or they can’t balance their professional life and their family life.”

At a time when a combination of forces – including Japan’s notoriously low birth rate – threaten to derail economic growth, this is not simply an issue for women. Kathy Matsui, chief Japan strategist at Goldman Sachs Japan, first coined the term “womenomics” in 1999, estimating that Japan could raise its gdp by 15 per cent if it got more women – the country’s “hidden asset” – into the workplace. Abe agrees. “Unleashing the potential of ‘womenomics’ is an absolute must if Japan’s growth is to continue,” he wrote in a newspaper article last year.

Hayashi showed the rest of Japan just what could be achieved with political will and the confidence to make the necessary budgetary decisions. The city shoulders four-sixths of the ¥1.5m (€11,000) it costs to put each child in nursery each year (the rest is split between the parents and the national government). “Our budget shortfall for 2013 was ¥41bn [€300m] so you have to be selective and concentrate resources where they’re needed,” she says.

If funding was one issue, finding the space to build new nurseries was another. Yokohama didn’t have enough vacant land. Each of the city’s 18 districts was allocated a person whose job it is to secure sites for new nurseries. Byobugaura Harukaze’s location under an elevated road was one solution. “We weren’t bound by stereotyped ideas,” says Hayashi. Smaller support centres have opened in vacant shops and empty classrooms. The city broke with convention by teaming up with partners from the private sector, non-profit organisations and social welfare corporations such as Harukaze, which operates Byobugaura.

The mayor also understood that the one-size-fits-all approach in public nurseries – five days full time or nothing – was another stumbling block to women returning to work. “People have different needs,” she says. “Maybe they only want to work part time or they need longer hours.” So she improved the variety of services on offer and introduced “nursery concierges” at City Hall to explain the options to parents. Subsidies were used to standardise the fee system, which had been particularly hard on parents who were allocated places in more expensive nurseries.

A “matching” system was also established, pairing up private landowners with nursery operators to open up more spaces for city nurseries. P’s Smile Nursery is a new nursery on the sixth floor of a commercial building that sits on top of JR Tsurumi station. The city brought together the owners of the building, East Japan Railway, with Doronkokai – a social welfare corporation that operates nurseries.

The nursery, which is open from 07.00 to 20.00, is at full capacity, with 54 children between the ages of nought and six. Temporary all-day care is offered for the remarkably low price of ¥1,300 (€9) while full-time day care is means tested and capped at ¥77,500 (€550) a month for under-threes and ¥43,500 (€308) for older children.

P’s Smile was designed by a team from Chiba University to give the children the best experience in a limited space. There’s a garden with a vegetable patch on the roof and children are taken out on bus trips to a farm in the countryside. “Usually, there’s no way we could provide this kind of service in the public sector,” says Doronkokai president Aika Yasunaga, who embarked on the nursery business 15 years ago when her own child was a toddler and she ran into problems with the childcare system.

Citing Hayashi’s success in Yokohama, Abe addressed the government’s ideas on childcare in his big policy speech last April, including plans to eliminate waiting lists across Japan by 2017, improve conditions for childcare providers and encourage employers to be open to three-year childcare leave, extending the window for women to return to work.

Keeping Yokohama’s waiting lists at zero will be a challenge and the search for more qualified childcare providers has gone nationwide – but Hayashi and Matsui agree that progress is being made.

“‘Womenomics’ and the diversity topic in general have finally become part of the national agenda,” says Matsui. “What everyone says is that in the ongoing war for talent they can no longer afford to see their talented Japanese female employees ‘off ramp’ [voluntarily leaving their careers]. Obviously Japan still has a long road ahead but at least the public focus and dialogue are shifting in the right direction.”

Hayashi has achieved astonishing results in Yokohama but thousands of children are likely to be on Japan’s waiting lists come the start of the school year on 1 April. “We’ve reached a point where we can’t leave it to local government,” she says. “The national government needs to do something to ease the burden.” For Hayashi it’s as much about choice as economic necessity. “I’m not saying that women have to work,” she says, “but they should be able to if they want to.”