BEIJING (AP) — From a waterfront concert in a Hong Kong park to a quiet candlelit prayer in a Melbourne alley, Liu Xiaobo's supporters around the world gathered Wednesday to mark the traditional Chinese observance of the seventh day after the imprisoned Nobel Peace Prize laureate's death.

Outside a leafy apartment complex in west Beijing, however, more than a dozen men have been holding an around-the-clock vigil with a different purpose altogether: keeping visitors and journalists away from the home Liu shared with his widow, Liu Xia.

Last seen in official photos showing her lowering an urn containing her husband's ashes into the sea on Saturday, Liu Xia's whereabouts remain unknown, sparking concerns from friends and demands by numerous foreign governments and rights groups that China lift all restrictions on her movement.

Liu Xia was never charged but has been kept guarded and largely isolated in the apartment for more than seven years while her husband served an 11-year sentence on charges of incitement to subvert government power after he published a manifesto calling for political reform.

Tienchi Martin-Liao, the president of the Independent Chinese PEN Center and a close family friend based in Cologne, Germany, said there were rumors that Liu Xia has been forced by authorities to take a "vacation" in the southwestern province of Yunnan, where she has friends. Liu Xia and her close circle of confidants in China have gone quiet, Martin-Liao said.

"Before we were able to at least see her weekly through video chat on a friend's phone. Now she's been completely cut off," Martin-Liao said. "What crimes has she committed to be surveilled, controlled and humiliated?"

During a brief visit to Liu Xia's apartment complex on Wednesday, there were no signs of supporters. The vast compound and each of its entrances were guarded by more than a dozen young men with buzz cuts who closely followed and filmed anyone who approached. Outside the compound's main gate, a handful of plainclothes agents had installed chairs and an umbrella to sit under while they watched, shooing away anyone who photographed them.

In semi-autonomous Hong Kong, perhaps the only corner of Chinese territory where it was possible, more than 1,000 people gathered Wednesday at Tamar Park for speeches and a rock concert to commemorate Liu. Nobel Committee chairwoman Berit Reiss-Andersen appeared in a video to pay tribute.

In recent days, authorities in mainland China have rigorously censored references to Liu Xiaobo on China's internet, with reports that social media posts containing candle emojis and the letters "RIP" have been censored for violating "relevant laws and regulations." WhatsApp, a Facebook-owned service used by Chinese dissidents for a degree of privacy, had patchy service this week as authorities periodically blocked access to its servers.

On Saturday, authorities accompanied by Liu Xia and a few relatives lowered Liu Xiaobo's ashes into the Pacific Ocean at Tiger Beach near Dalian, a move that his supporters said was designed to erase any physical traces of China's best-known political prisoner and prevent the transformation of Liu's grave into a memorial site. For centuries the practice of cuoguyanghui — literally "file down the bones and scatter the ashes" — was known as a cruel form of posthumous punishment in traditional Chinese culture, which placed importance on being laid to rest in tombs that could be visited and venerated by descendants and loved ones.

Liu's supporters have sought to commemorate him by visiting beaches, to the dismay of authorities. Ye Du, a close friend, told Hong Kong media on Wednesday that police arrived at his home bearing fruit and cigarettes in an effort to cajole him not to go near "rivers and oceans."

On Tuesday afternoon, police took away Jiang Jianjun, a Dalian man who had posted online about scattering flowers at Tiger Beach, his wife told The Associated Press.

Outside China, supporters gathered on beaches to mourn while others turned Liu's sea burial into a meme as people on Wednesday posted pictures of an empty chair — a reference to Liu's unoccupied seat at the Nobel Peace Prize ceremony in 2010 while he was imprisoned — next to bodies of water.

Zhou Fengsuo, a California-based activist involved in the 1989 Tiananmen student-led pro-democracy protests in which Liu Xiaobo played a key role, posted pictures of himself this week holding the Lius' portrait while chest deep in San Francisco Bay.

"Many of us were angry, like there was nothing we could do because it was a sea burial," he said. "But when I swam, I felt like we had a connection, like he was there."

In Australia, supporters held a candlelight vigil in Melbourne in an alley where a dissident artist known as Badiucao had drawn a picture of Liu.

Other supporters found creative ways to mourn online. On a popular Chinese music streaming service, users this week left a string of comments about a song titled "The Ocean" by the late Taiwanese pop singer Chang Yu-sheng. Some mentioned Liu's name while others were more oblique in their messages.

"Floating with ocean currents, you'll never be forgotten," one said, while another said, "They think it's over, but they don't know that every place that the waves will touch will hold your memory."

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AP videojournalist Josie Wong in Hong Kong contributed to this report.