In a post on Instagram late on Monday, the artist indicated that he had found himself barred from entering Switzerland upon arrival from London.

"I am sleeping on a bench with a blanket tonight, waiting to be deported next morning at 6:50 am," he wrote.

Early on Tuesday, he posted a video showing him being driven through an all but deserted Zurich airport terminal before his departure back to London.

Asked about the case, Zurich cantonal police told AFP that they had "discovered that Mr. Weiwei, as a Chinese national, did not have the necessary travel documents".

"For this reason, he was denied entry into the Schengen area," Europe's open-borders zone, a spokesman said in an email.

"As is common in such cases, Mr. Weiwei remained in the transit area until his return flight to the airport of origin," police said, stressing that the artist "was never arrested and was always able to move freely".

The son of a poet revered by former communist leaders, 67-year-old Ai is perhaps China's best-known modern artist and helped design the famous "Bird's Nest" stadium for Beijing's 2008 Olympics.

But he fell out of favour after criticising the Chinese government and was imprisoned for 81 days in 2011. He eventually left for Germany four years later.

The artist, who has been living with his son in Portugal since 2019, has visited Switzerland previously to take part in cultural events and to present exhibits, with his most recent visit reportedly taking place in 2023.