China's parliament unanimously handed President Xi Jinping a second term Saturday and elevated his right-hand man to the vice presidency, giving him a strong ally to consolidate power and handle US trade threats.

Xi's reappointment by the legislature was a foregone conclusion, but all eyes had been on whether his former anti-corruption enforcer, Wang Qishan, would become his deputy.

The National People's Congress has widely expanded Xi's already considerable authority during its annual session, adding his name to the constitution and lifting the two five-year term limit for the presidency and vice presidency.

Xi received a standing ovation after winning all 2,970 votes. Only one delegate voted against Wang's appointment, with 2,969 in favour. In 2013, Xi had received 2,952 votes, with one against and three abstentions, a 99.86 percent share.

Xi and Wang shook hands as the legislators applauded.

As part of the package of constitutional amendments, Xi and Wang for the first time took the oath of office by pledging allegiance to the constitution. Xi put his left hand on a red-covered book containing the constitution, and raised his right fist to take his oath.

Elevating Wang allows Xi to keep a formidable ally by his side, as China's most powerful leader since Mao Zedong cements his authority and sets his sights on a possible lifelong tenure.

Wang, 69, stepped down from the Communist Party's ruling council in October under informal retirement rules.

But he has kept a prominent profile, sitting at the same table as the seven members of the Politburo Standing Committee during the public sessions of the National People's Congress.

Wang's appointment shows that "he's a really important political advisor," said Kerry Brown, director of the Lau China Institute at King's College London.

"He's a very capable politician, so it make sense he would still be around," Brown told AFP, noting that "it also shows we're in an unconventional time in Chinese politics."

Wang was at the frontline of Xi's anti-corruption crusade, heading the party's Central Commission for Discipline Inspection, which punished 1.5 million officials in the past five years, from low-level cadres to regional leaders and generals. He stepped down last year.

Known internationally in his previous role as China's pointman on trade, Wang could help Xi deal with increasingly tense relations with the United States amid fears of a looming trade war, analysts say.

Chinese President Xi Jinping walks with his ballot before a vote at the fifth plenary session of the National People's Congress (NPC) at the Great Hall of the People in Beijing, China March 17, 2018. Photo: Reuters

'Dream team'

Xi's real power stems from his title as general secretary of the Communist Party, but analysts say Wang could provide extra heft to his presidency, even though the vice president has largely been a ceremonial post.

Xi is keeping Wang by his side because of his "talent and ability," according to Hua Po, an independent Chinese political commentator.

"Choosing Wang as vice president is certainly to consolidate his power," Hua told AFP.

"Xi is already a very powerful man. The problem is that he has too few people who are loyal and competent for his use, so he has to retain Wang and give himself more time to cultivate more talented people."

Wang replaces Li Yuanchao, a relatively low-profile politician who has represented Xi on trips abroad.

When he was vice premier, Wang periodically travelled to the United States, where then-president Barack Obama once gave the Chinese delegation a signed basketball that the official held up at a press conference.

An "amazing" economist, he could now form a "dream team" with another member of the party leadership, Wang Yang, to deal with concerns that US President Donald Trump policies will trigger a trade war, Brown said.

"Maybe they'll be able to come up with a solution for this massive brewing storm with America about imbalances and tariffs."