After months of being told to strip off to keep cool for summer, Japanese workers were Tuesday being urged to wrap up for winter in an energy-saving "Warm Biz" campaign.

As the nation continues to face possible electricity shortfalls in the wake of the Fukushima nuclear disaster that has left dozens of atomic reactors offline, the government is asking people to keep warm the old-fashioned way.

Officials are telling homes and offices to set heaters and air conditioners no higher than 20 degrees C (68 F).

Average temperatures in Tokyo fall to around six degrees C in January and February and the government is advising people to wear extra layers of clothes and eat hot meals to keep out the cold.

Using a cartoon ninja character, the environment ministry suggests putting on scarves, gloves and leg warmers during the day and an extra layer after the evening bath, or wearing a towel around the neck in bed.

For dinner, it recommends a traditional Japanese hotpot.

"You can lower the heat if you enjoy 'nabe' with your family and friends, making both bodies and the room warm. The temperature will feel higher than it actually is thanks to steam from the pot," the ministry website says.

Eating root vegetables and ginger will help to "warm the body up", it says, adding that getting off the train a stop earlier and walking the rest of the way to work will boost circulation.

Companies have also got in on the act, with adverts on the Tokyo subway extolling the energy-saving virtues of home appliances and reminding commuters to keep the dial turned down.

Clothing giant Uniqlo has stocked up on thermal underwear and department stores are promoting a range of knit wear to stave off the winter chills, the Yomiuri newspaper reported.

More off-the-wall ideas include a suggestion from brewer Kirin that beer drinkers microwave their stout-style brew and add sugar or spices.

The campaign, which runs until March, comes as Japan eyes a potential electricity shortfall over the cold winter months with the bulk of nuclear generators, on which resource-poor Japan is heavily dependent, still offline for safety checks amid public disquiet over the technology.

Japan's hot summer months were marked by a heightened "Cool Biz" campaign -- aimed at limiting air conditioner use and encouraging workers to ditch jackets and ties.

Local governments prohibited overtime and factories changed shifts to make use of cooler evenings, early mornings and lower-demand weekends. In one region, employees were told to take a two-hour siesta after lunch as the nation pulled together to stretch out the available electricity and avoid blackouts.

Consumers in Japan have long been used to a plentiful and reliable electricity supply that powers everything from garish neon signs to heated toilet seats.