The pollution in China is so bad that 25,000 people went to photograph a clear sky

On Friday, a 25,000-strong crowd reportedly gathered in China's capital to photograph a rare sight - a clear blue sky.

People's Daily, the Chinese government's official newspaper, wrote that thousands had gathered in Beijing's Jingshan Park to photograph the "long-missed azure skies".

Separate posts on Instagram hailed how the park looked on "beautiful, pollution free days."

Air pollution is a severe issue in China, with smog levels in Beijing, Shanghai, Guangzhou and Xi’an all exceeding the World Health Organisation's guidelines. According to the Global Burden of Disease Study, the air pollution contributed to 1.2 million premature deaths in China in 2010.

Curbing pollution, particularly from coal-burning factories, remains a daunting challenge for the country. Smog is also becoming an increasingly political problem for China's ruling elite. Earlier this year Chinese authorities banned a popular documentary investigating the effect of pollution Under the Dome.

More: This video shows how bad the smog problem is in China