China's rubber-stamp 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 Communist Party-controlled 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 for the presidency and Central Military Commission chairman. In 2013, Xi had received 2,952 votes, with one against and three abstentions, a 99.86 percent share.

Only one delegate voted against Wang's appointment, with 2,969 in favour.

Xi and Wang shook hands as the legislators heaped on applause.

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 charter, and raised his right fist to take his vow.

"I pledge loyalty to the constitution of the People's Republic of China" Xi recited, vowing to "strenuously struggle to build a rich, strong, democratic and civilised" country.

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 -- a move that has drawn criticism online.

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 while receiving fervent applause from the delegates as he voted.

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 makes 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 has 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.

'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 in the past.

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.

In his former position as vice premier, Wang periodically travelled to the United States, where then-president Barack Obama once gave the Chinese delegation a signed basketball.

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."

Great happiness

China's capital was engulfed in a rare flurry of swirling snow on Saturday, sending delegates of the congress scurrying from the Great Hall of the People after the vote.

Legislators beamed when talking about Xi -- a stark contrast from the criticism that Chinese people expressed online when term limits were lifted last week, prompting censors into action.

"Our Chairman Xi is too great, truly he is too great," said Du Meishuang, a Chinese opera singer and delegate from Chairman Mao's home province of Hunan.

"I hope he will rule for life, truly, this is the common people's heartfelt wish."

She said the single vote against his deputy Wang was not a problem: "His age is quite advanced, maybe that was the reason."

"All Chinese are looking forward" to Xi continuing on, said Zhang Fanhua, a delegate from Anhui, as he hurried into the falling snow.

"This is a great happiness for the country and the nation."