Image copyright Sotheby's

A 1937 letter from Chinese Communist Party leader Mao Zedong to then-Labour Party leader Clement Attlee has sold at auction for £605,000 ($918,000).

In the letter, Mao asks Attlee for "practical assistance" in battling Japanese troops who had invaded China.

Auctioneers Sotheby's said the historical letter was an "exceptionally rare" example of Mao's signature.

The lot far exceeded its £100,000-150,000 estimate and was bought by a Chinese private collector.

Call for help

In the typed letter signed by Mao, the communist leader tells then-opposition leader Mr Attlee: "We believe that the British people, when they know the truth about Japanese aggression in China, will rise in support of the Chinese people, will organise practical assistance on their behalf, and will compel their own government to adopt a policy of active resistance to a danger that ultimately threatens them no less than ourselves."

Image copyright Sotheby's Image caption Mao told Attlee in the letter that the correspondence was "a message of goodwill"

The letter was written from Yan'an in north-west China, where the communists set up their headquarters following the Japanese invasion.

Sotheby's said the timing of the communication was significant because Attlee had started to lead the party away from its "long-held pacifist position", and became "a major critic of the Conservative government's policy of appeasement towards Nazi Germany and her allies".

A 'curiosity'

Mao's letter was sent to Atlee by the journalist James Bertram, who added an accompanying note to Attlee advising the British politician to "keep the enclosed letter, if only as a curiosity".

Gabriel Heaton, Sotheby's specialist in books and manuscripts said the letter was "an extraordinarily early instance of Mao engaging in international diplomacy, and is an exceptionally rare example of Mao's signature".

He added it was "only the second document signed by Mao to appear on the international auction market in recent decades."

The sale, in London, comes after several weeks of interest in China following the much-publicised four-day visit to the UK by Chinese President Xi Jinping in October.

Chinese history gained further attention last month when Labour shadow chancellor John McDonnell threw a copy of the Chinese Communist Party leader's Little Red Book at Chancellor George Osborne in Parliament, claiming UK assets were being sold to the Chinese.

Elsewhere on Tuesday, a red prime ministerial dispatch box belonging to the late Margaret Thatcher has sold at auction for £242,500.

Image caption The shadow chancellor threw Mao Zedong's Little Red Book at George Osborne in Parliament last month

Who was Mao Zedong?

Born in 1893, Mao Zedong was one of the founders of the Chinese Communist Party and was an influential 20th Century thinker.

He helped build the Red Army, led it on a 6,000-mile "long march" to escape its nationalist foes, and emerged as the most powerful party figure.

After victory over the nationalists in 1949, Mao proclaimed the People's Republic of China and became its first leader. His policies resulted in the deaths of tens of millions of people.