Two pro-independence Hong Kong lawmakers lost their appeal Wednesday against a ban preventing them from taking up their seats in parliament as Beijing faces accusations of stepping up interference in the city's politics.

Baggio Leung and Yau Wai-ching deliberately misread their oaths of office, inserted expletives and draped themselves with "Hong Kong is not China" flags during a swearing-in ceremony in October.

Speaking after Wednesday's judgement, an angry Leung said the "invisible hand" of Beijing had intervened in Hong Kong's affairs.

Leung and Yau were voted in to parliament in citywide polls in September which saw several rebel candidates take seats for the first time, advocating either independence or self-determination for Hong Kong.

The new movement supporting a possible split from Beijing for the semi-autonomous city has gained traction as young pro-democracy campaigners grow increasingly frustrated with a lack of political reform.

Beijing hit out at the pair in a special "interpretation" of the city's constitution earlier in November that effectively prevented them from taking up their seats because of the way they took the oath.

Following Beijing's protest, Hong Kong's High Court ruled the two lawmakers should be disqualified from the legislature because their oaths were invalid, in an unprecedented judicial review brought by the city's leader and justice secretary.

Yau and Leung appealed, but lost out Wednesday in a judgement that took Beijing's ruling into account, amid criticism that the separation of powers in Hong Kong has been compromised.

The Court of Appeal's judgement referred to Beijing's ruling as giving the "true meaning" to the part of the constitution that requires lawmakers to take an oath of allegiance to Hong Kong as a special administrative region of China.

The judgement said the court's duty to apply the city's constitution, known as the Basic Law, outweighed the doctrine of separation of powers and non-intervention.

- 'Political suppression' -

Yau and Baggio were originally offered a second chance at taking the oath by the president of the legislature, but Beijing stepped in to prevent that.

Its special interpretation of the Basic Law ruled that any oath-taker who does not follow the prescribed wording of the oath, "or takes the oath in a manner which is not sincere or not solemn", should be disqualified.

Wednesday's appeal judgement said there could be "no dispute" that Yau and Leung had declined to take the oath.

Leung said he did not believe he had done anything wrong.

"The way the oath incident has developed from an affair within Hong Kong to what it is now is unexpected to us all," he told reporters.

Leung said the pair were actively considering their next step but had not decided whether to proceed to the Court of Final Appeal.

The judgement came as the government announced plans to take a third newly elected lawmaker to court over her oath-taking.

The department of justice said it would initiate proceedings against teacher Lau Siu-lai, a prominent activist who made her name during the city's mass pro-democracy rallies in 2014 and now advocates self-determination for Hong Kong.

It gave no further detail on the grounds for the case.

Lau's oath was rejected during her swearing in as she read the pledge at a snail's pace, leaving long gaps between every word.

She was later given a second chance to read it and was able to take up her seat.

Lau slammed the decision to take her to court as "political suppression".