"The vice-president looked in great health," said a professor in the university's electrical engineering department, who accompanied Xi for most of his visit. "It was hot outside and he didn't even sweat that much."

State television showed Xi smiling and walking without any need of support. He was shown engaged in conversation with teachers and students.

Xinhua also issued reports of his visit with pictures.

Professor Zhang Ming, a political scientist with Renmin University, said Xi's return would put an end to the rumours. "He's back and everything is fine," Zhang said.

Xi disappeared from public view on September 1 after delivering a speech at the Party School. His failure to meet visiting US Secretary of State Hillary Rodham Clinton and Singaporean Prime Minister Lee Hsien Loong in the following days prompted questions at home and overseas about the 59-year-old's health - and whether he would take over at the party's 18th national congress, likely to be held next month.

With no official explanation for Xi's absence, rumours began to circulate that he was resting after injuring his back, or had fallen seriously ill.

The silence was broken on Wednesday when media including China News Service reported that Xi had expressed condolences to the family of a party veteran who died recently.

Teachers and students at the university who saw Xi yesterday said he appeared to be in robust health. The vice-president arrived on the campus at about 9.30am and stayed outside for about 40 minutes. His speech was about agriculture technology and food safety. Xi shook hands with a dozen elementary school pupils and encouraged them to study hard, the teachers said.

Beijing-based political analyst Chen Ziming said the party was sticking to the outmoded practice of treating the health of state leaders as secret.

But he said that Xi's reappearance at least showed the party congress would get "under way as expected".

Also attending the university function was Ling Jihua, formerly the closest aide of President Hu Jintao.

It was Ling's first public appearance since losing his position this month as director of the Central Committee's General Office. He now heads the party's United Front Work Department.

Unlike other principal officials, Ling was not shown on state television's main newscast.

Li Daoliang, a professor, said Ling stopped at a display showing advances in aquaculture technology.

He was amazed to know that Chinese fishermen could use smartphone applications to assist them, the professor said.

Timeline: Xi Jinping reappears

September 1: Xi Jinping, president of the Central Party School, addresses a ceremony in Beijing marking the start of its autumn semester.

September 5: Xi cancels scheduled meetings with US Secretary of State Hillary Rodham Clinton and Singaporean Prime Minister Lee Hsien Loong. The Foreign Ministry says the cancellation of the Clinton meeting was a "normal adjustment of the itinerary".

September 8: Xi is absent, according to an official account, from an emergency meeting of the Central Military Commission to discuss how the army will respond to earthquakes in Yunnan province.

September 10: Xi skips a pre-announced meeting with Danish Prime Minister Helle Thorning-Schmidt.

September 13: Xi expresses condolences to the family of a veteran Communist Party official who died a week earlier, the official Guangxi Daily reports. The report does not say when Xi sent his condolences and does not quote him or include a picture of him.

September 14: Reuters reports that Xi could make a public appearance as early as Saturday as he recovers from a bad back, cited from sources.

September 15: Xi reappears in public, attending an activity to mark National Science Popularisation Day at China Agricultural University.