Hu, 79, Xi Jinping's immediate predecessor, had been seated to the left of Xi on Saturday before he was led off the stage of the main auditorium of the Great Hall of the People in Beijing by two stewards, a Reuters witness at the congress said.
Video footage published by AFP showed a steward repeatedly trying to lift Hu from his seat, drawing concerned looks from officials seated nearby. Hu then put his hand on a sheet of paper placed on Xi's folder but Xi quickly put his hand on the sheet.
China's top legislator Li Zhanshu, seated to Hu's right, gave the former president's folder to a steward, wiping his own head with a cloth after Hu finally stood up.
Looking distressed, Hu appeared to resist leaving as the stewards escorted him out, turning back to his seat at one point. On his way out, he exchanged words with Xi and patted Premier Li Keqiang, seated to the right of Xi, on the shoulder.
Video of the incident, highly unusual given the meticulous stage management of most such events, was widely shared on Twitter but could not be found on China's heavily censored social media platforms. Twitter is blocked in China.
On China's Twitter-like Weibo, a few social media users alluded to the incident by commenting on old posts featuring Hu, a common tactic used to evade cyberspace censors.
By Saturday evening, however, the comments section of almost all Weibo posts containing Hu's name were no longer visible, according to a Reuters review.
State media coverage of the ceremony did not include the scene, which occurred as journalists were entering the hall.
The official CCTV evening news coverage of Saturday's congress closing ceremony included footage with Hu, as normal, from before the incident.
Hu had appeared slightly unsteady last Sunday when he was assisted onto the same stage for the opening ceremony of the congress.
Late on Saturday, China's official news agency Xinhua tweeted about the incident.
"Xinhuanet reporter Liu Jiawen has learned that Hu Jintao insisted on attending the closing session of the Party's 20th National Congress, despite the fact that he has been taking time to recuperate recently," it said.
"When he was not feeling well during the session, his staff, for his health, accompanied him to a room next to the meeting venue for a rest. Now, he is much better," a second tweet said.
There was no mention of Hu on Xinhua's domestic Weibo postings.
The once-in-five-years congress concluded with amendments to the party's constitution that cements the core status of Xi and the guiding role of his political thought within the party.Â
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