Japan launched its annual "Cool Biz" campaign on Friday, an energy conservation drive that calls on business people to ditch their jackets and ties so offices can keep air conditioning to a minimum.

Many workers in Tokyo could be seen dressed down while some government officials took the message to heart by showing up to work in Okinawan-style collared t-shirts.

Temperatures in the capital were hovering in the mid-20 degrees Celsius range, but the mercury can climb into the high thirties during summer with energy-sapping humidity.

Now in its 11th year, the summer-long campaign asks offices to set their air con at no cooler than 28 degrees Celsius (82 degrees Fahrenheit).

The tradition was embraced by non-Japanese offices too -- the British embassy sent out a message on social media to let visitors know they can dress down.

"Please feel free to dress in Cool Biz style when you visit the British Embassy Tokyo," it said on Twitter.

The campaign took on a new significance after the 2011 Fukushima nuclear accident when Japan scrambled to plug the energy gap left by switching off atomic reactors that once supplied more than a quarter of Japan's power.

Clothing companies have cashed in on the dress-down summer fashion trend, as conservatively dressed corporate soldiers, usually clad in dark suits, turn to spiffy, button-down shirts.

But not everyone is happy -- tie-makers complain about falling demand for their wares.