The Great Wall of China has been officially declared even longer than previously thought, state-run media report.

The wall measures 21,196.18km (13,170.6956 miles) long based on the latest state survey results, state-run news agency Xinhua reported on Tuesday.

A preliminary study released in 2009 estimated the wall to be 8,850km long.

The world's largest man-made structure was built to protect China's northern border.

This is the first time such a definitive figure has been released, Xinhua reports.

The State Administration of Cultural Heritage released the results based on an archaeological survey done since 2007.

Previous estimates of the wall's length were mainly based on historical records.

Tong Mingkang, deputy chief, said that the survey revealed a total of 43,721 heritage sites that included stretches of the Great Wall, reports Xinhua.

Known to the Chinese as the "Long Wall of 10,000 Li", the Great Wall is a series of walls and earthen works begun in 500BC and first linked up under Qin Shi Huang in about 220BC.

Only 8.2% of the original wall remains intact, with the rest in poor condition, according to the report.

It was listed as a Unesco world heritage site in 1987.