Zimbabwe's cabinet backed draft legislation on Tuesday that would change the constitution to extend presidential terms from five years to seven, allowing President Emmerson Mnangagwa to stay in office until 2030.

Other proposed changes in the bill presented to cabinet include a provision that the president be elected by parliament rather than through a direct popular vote.

Justice Minister Ziyambi Ziyambi told a news briefing that the bill would be sent to the speaker of parliament and published in an official gazette before lawmakers consider it.

Mnangagwa, 83, is currently meant to step down in 2028 after serving two five-year terms, and there has been a succession battle in the ruling ZANU-PF party over who will take over.

He came to power after a military coup ousted longtime leader Robert Mugabe in 2017, and opposition politicians have condemned moves by his party to extend his time in office.

Jameson Timba, a senior leader in the southern African country's fractured opposition movement, said in a statement that the cabinet's approval of the changes was "politically destabilising".

He said a group called Defend the Constitution Platform would immediately consult lawyers and brief regional and international partners as part of efforts to oppose the changes.

ZANU-PF has ruled Zimbabwe since independence from Britain in 1980.

It has a two-thirds majority in the lower house of parliament and also overwhelmingly controls the upper house through traditional leaders and other proxies who generally vote with it, allowing it to change the constitution.