The government began its annual "Cool Biz" campaign on Friday, promoting energy conservation by allowing workers to dress casually, though its offices were staffed with fewer people this year as many were working from home amid the spread of COVID-19.

The initiative that will extend through the end of September, and which first ran in 2005, calls for air conditioners to be set at 28 Celsius. Officials can ditch jackets and ties for casual clothing such as polo shirts and even Hawaiian aloha shirts.

"I hope the (air conditioner) temperatures will be set adequately in homes too," Environment Minister Shinjiro Koizumi told a news conference, referring to those teleworking amid the virus pandemic.

In the Kasumigaseki district of Tokyo, where government ministries and agencies are concentrated, some had their jackets off on their way to the office as the temperature reached 21.9 C at 9 a.m.

At the Environment Ministry, where about 70 percent of officials were telecommuting, some of those in the workplace were wearing shirts in Okinawa's famed kariyushi summer style — similar to Hawaii's aloha shirts — to keep cool.

The ministry is calling on workers to dress casually at their own discretion in October if the heat continues. It plans to no longer set the campaign period from next year, given that a variety of working methods, including telework and staggered commuting, have taken root.

In previous years, the ministry has also promoted its "Cool Share" campaign aimed at getting people together in air-conditioned common spaces, including public and commercial facilities and cafes, but decided not to encourage it this year because it could generate crowds and so raise the risk of virus infections.