Police handed Chinese dissident artist Ai Weiwei back his passport on Wednesday four years after it was confiscated, he told AFP, hailing the move with a smiley emoticon.

Ai is China's best known contemporary artist abroad, but authorities have denied him a passport since 2011 in an apparent attempt to limit his international influence.

The bearded conceptualist was detained for 81 days in 2011 amid a nationwide crackdown on dissent, with authorities continuing to hold the travel document after he was released.

But Ai on Wednesday published a photograph of himself clutching a red Chinese passport online, with the words: "Today, I received a passport."

Confirming to AFP that the photograph showed his own document, he responded to inquiries with a text message consisting of a smiley emoticon.

Police told him: "This is yours, we are returning it to you," he added in another SMS.

It came 600 days after he started protesting over the issue by placing flowers in a bicycle basket outside his Beijing studio, leading to the creation of the social media hashtag #flowersforfreedom.

It is not clear whether having a passport means that Ai will be able to travel freely. Many Chinese dissidents have been detained at airports while trying to leave the country.

However the Royal Academy of Arts in London said it expected Weiwei would travel to Britain ahead of his exhibition opening there on September 19.

"Ai Weiwei has just received his passport from the Chinese authorities and is now free to travel outside of China," said artistic director Tim Marlow.

"We are delighted to announce that he will be joining us as we finalise the installation of his exhibition at the Royal Academy of Arts, London."

The exhibition, which opens on September 19, will be "the first major institutional presentation of his work in the UK," Marlow added.

Ai has continued to hold exhibitions overseas despite being unable to travel, last year designing a huge installation on the former prison island of Alcatraz near San Francisco.

The artist, who has released a heavy metal album and cites French artist Marcel Duchamp -- seen as the father of conceptual art -- as an inspiration, is known for his irreverent humour.

His outspoken criticism of China's ruling Communist party has seen his work censored domestically.

But last month authorities allowed his first solo exhibition in the country to open in Beijing. It consisted of a reconstructed 400-year-old wooden ancestral hall.

The show lacked Ai's usual political commentary, but the state-run Global Times newspaper in an editorial called on him to "change his politics".

The son of a poet revered by China's first generation of Communist leaders, Ai helped to design the Bird's Nest Olympic Stadium for the 2008 Beijing Games, an event that brought the ruling party worldwide prestige.

But the burly artist's outspoken criticism of China's leaders -- he has referred to them as "gangsters" -- and involvement in controversial social campaigns went on to make him a thorn in the government's side.