Rumoured to have died a few months ago, 91-year-old former Chinese president Jiang Zemin roused social media users Wednesday by taking a prominent place at the ruling Communist Party's leadership Congress.

Proving that reports of his death were greatly exaggerated, the former leader sat next to President Xi Jinping and stood for the national anthem as the twice-a-decade congress opened with a speech by Xi in Beijing's vast Great Hall of the People.

Many Chinese internet users gushed over the elderly "Frog", an affectionate nickname inspired by Jiang's wide grin and prominent bespectacled eyes, marvelling over the apparently still hale nonagenarian in postings sprinkled with frog emojis.

"I want to ask about his secret for longevity," said one posting on China's Twitter-like social network Weibo.

"How many organs must he have had replaced to be standing in the middle of the stage?" asked another.

Jiang, the former party leader and Chinese president for a decade from 1993, is occasionally the subject of rumours of his demise.

The most recent came in May amid a flurry of online speculation that he had died of a stroke in Shanghai, the commercial hub that Jiang formerly governed as mayor and party chief.

Past presidents are typically on hand for the congress, during which the top leadership and party policies for the next five years are set in stone, and Jiang's immediate successor Hu Jintao, 74, was on Xi's right hand.

Jiang, a former factory engineer, came to power in the traumatic aftermath of the 1989 Tiananmen Square crackdown and led China through an era of stunning economic transformation.

Jiang's legacy remains mixed, as his term set the blueprint for rapid economic growth that gave rise to ills such as rampant environmental degradation and a widening wealth gap, which today's leaders are grappling with.

But with his big smile, grasp of several languages, and sometimes clownish behaviour including making jokes in English, Jiang is fondly remembered as a relatively colorful figure compared to his stiff successors Hu and Xi.

A music lover who played the piano, Jiang was known for bursting into song on foreign trips, including a memorable rendition of Elvis Presley's "Love Me Tender" during a state visit to the Philippines.

"Holy (expletive)! He is getting younger than ever," said one Weibo posting.

Jiang's presence was largely ignored by state media, however. 

Official mention of past leaders has become increasingly rare under Xi, who took power in 2012 and moved swiftly to clamp down on dissent as party mouthpieces push a cult of personality around him.