Zimbabwe's governing Zanu-PF party has won all six of Saturday's parliamentary by-elections meaning it now holds a two-thirds majority in parliament.

The victories give President Emmerson Mnangagwa the power to change key provisions in the constitution.

The opposition Citizens Coalition for Change (CCC) allege this will allow him to tighten his grip on power.

The by-elections were triggered after a man the CCC describes as an imposter forced the recall of some of its MPs.

Though the CCC lost last August's general election, it took more than 100 of the 280 seats in the National Assembly, thus denying Zanu-PF a super-majority.

But then in October, Sengezo Tshabangu, a name that up to that point was unknown to most people in Zimbabwe, wrote to the parliamentary speaker alleging some CCC MPs had "ceased to be members of the party".

The party's leader at the time, Nelson Chamisa, immediately labelled Mr Tshabangu a fake and told the speaker to ignore the letter.

But it was Mr Chamisa who was ignored as the speaker duly declared vacancies in the constituencies.

Saturday's votes were the second set of by-elections to be held after Mr Tshabangu's controversial intervention.

Last month, Mr Chamisa quit the CCC, which he had formed just two year ago, accusing Zanu-PF of infiltrating his party.

He alleged that the CCC had been "contaminated" and "hijacked" by the government.

"I will have nothing to do with sewer politics," the opposition leader said in a long statement.

Two lawmakers have since resigned from parliament in solidarity, meaning that further by-elections will be held.

President Mnangagwa came to power in 2017 following a bloodless coup that ousted long-time leader Robert Mugabe.

At the time he was seen as a beacon of change and hope for the struggling country.

But high inflation, unemployment and censorship remains rife in Zimbabwe.