Lights went out across Hong Kong on Saturday night for the 10th annual Earth Hour. Organisers, the World Wildlife Fund, said that millions of people from 178 countries and territories took part.

However, when buildings across the city’s glittering harbourfront dimmed their lights, there was a notable exception in the People’s Liberation Army garrison headquarters. Netizens noted that lights at the PLA building continued blazing.

Photo: Kylie Leung, via Facebook.

The Tourism Board’s Symphony of Lights performance was cancelled to mark the event.

Ahead of the switch-off, Chief Executive Leung Chun-ying said that all government departments would begin switching off outdoor lights from 11pm onwards each day.

Earth Hour is a global, yearly effort to encourage households, businesses, communities and individuals to turn off non-essential lighting for an hour between 8:30pm and 9:30pm.

Photo: Stephanie Chan, via WWF.

The movement began in Sydney, Australia, in 2007 and now includes more than 7,000 cities and towns across the world.

The initiative calls upon people to reduce their energy consumption and adopt more sustainable lifestyles.