Hong Kong rebel lawmakers swore, shouted, banged drums and railed against "tyranny" Wednesday when they took their oaths of office in the city's parliament, as calls grow for a split from Beijing.

The chaotic first meeting of the new term of the Legislative Council (Legco) came after a citywide vote last month saw victories for several lawmakers advocating more autonomy or even independence for Hong Kong.

The city is semi-autonomous under a "one country, two systems" deal sealed when Britain returned Hong Kong to China in 1997.

The arrangement protects Hong Kong's freedoms for 50 years, but there are increasing concerns those liberties are disappearing as Beijing tightens its grip.

Lawmakers are required to recite a short oath in Legco before they can officially take up their seats.

That oath declares repeatedly that Hong Kong is a "special administrative region" of China.

The government had warned lawmakers in advance they risked losing their seats if they did not take the oath properly.

Nathan Law, 23, Legco's youngest lawmaker and a former pro-democracy protest leader, delivered an impassioned speech ahead of taking the oath.

"You can chain me, you can torture me, you can even destroy this body - but you can never imprison my mind," he said, quoting India's independence leader Mahatma Gandhi.

Law, who is calling for self-determination for Hong Kong, was one of the main leaders of the 2014 Umbrella Movement rallies which brought tens of thousands to the streets calling for democratic reform.

Two new pro-independence lawmakers, Baggio Leung and Yau Wai-ching, added their own words before the oath, pledging to serve the "Hong Kong nation".

Both displayed flags emblazoned with the words: "Hong Kong is not China".

Leung took the full oath in English but refused to pronounce "China" correctly, instead calling it "Cheena".

Yau was distinctly heard saying "the People's Re-fucking of Zeena", instead of "the People's Republic of China" in her oath, although she denied that later, blaming her accent.

Local media reported that they had used the word "Shina" instead of China, an archaic, derogatory Japanese term for the mainland.

- Risk to seats -

New lawmaker Eddie Chu, who advocates a public referendum on Hong Kong's future sovereignty, shouted "Democratic self-determination! Tyranny will perish!" after taking his oath.

Teacher Lau Siu-lai, also a former Umbrella Movement activist, read every word of the oath at a snail's pace, prompting some pro-Beijing lawmakers to walk out.

The Legco clerk told Leung, Yau and one other pro-democracy lawmaker that he was unable to "administer" their oaths, because they had modified them.

It is not yet clear whether any of the lawmakers deemed not to have taken the oath properly will be barred from taking up their seats.

In a statement issued before the oath-taking, the government cited a law that stipulates "any person who declines or neglects to take an oath duly requested which he or she is required to take shall vacate office or be disqualified from entering on it".

The session was suspended after Law refused to return to his seat, questioning why the clerk had objected to the three lawmakers' oaths.

According to government rules, the clerk must now refer the invalid oath cases to the Legco president, who was elected Wednesday afternoon amid further chaos.

The three lawmakers who did not have their oaths approved were told they could not vote for Legco president.

The vast majority of pro-democracy lawmakers left the chamber before the vote, with some shouting and tearing up their ballots.

Pro-Beijing legislator Andrew Leung was voted in by 38 to zero by establishment lawmakers, who are in the majority in the Legco.

The pro-democracy camp had objected to his candidacy.

Separately Wednesday, Britain urged Hong Kong to protect rights and freedoms in the city in its regular six-monthly report.