Zimbabwe is holding by-elections in which there have been attempts to exclude the main opposition candidates - as President Emmerson Mnangagwa cements his control.

The vote was triggered after some opposition Citizens Coalition for Change (CCC) MPs had their seats declared vacant.

This was engineered by someone claiming to be the party's secretary-general.

The outcome could give the government an overwhelming majority.

The CCC lost August's general election but won more than 100 of the 280 seats in parliament. This denied the ruling Zanu-PF party a two-thirds majority that would enable it to change the constitution.

And there are people who suspect that the party has played a role in forcing these by-elections in constituencies where it recently lost.

But the CCC is plagued by factional conflicts and the current crisis appears to a large extent to be self-inflicted.

The reason this all matters is that President Mnangagwa's party is just a few seats short of a two-thirds majority in parliament.

Once it crosses that threshold, constitutional changes can be pushed through. It would be no great surprise if there is soon talk of abolishing presidential term limits.

Zimbabweans had hoped the downfall of Robert Mugabe six years ago would see the country go on a more democratic path.

What is surprising is some within the opposition appear to be helping concentrate power in the president's hands.

In October, Sengezo Tshabangu, a name 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 CCC leader, 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 by-elections are a result of that.