Opposition leader Morgan Tsvangirai says his MDC party will take part in an anti-government protest on March 22 because Zimbabwe's ruling party wants to "steal" the next election.

"We fully endorse the resolution that we took with others under the banner of [the National Electoral Reform Agenda, an umbrella grouping] to mobilise Zimbabweans for a public protest on the 22nd of March," Tsvangirai told reporters in the capital on Thursday.

A copy of his speech was seen by News24.

The opposition leader - who celebrates his 65th birthday on Friday - accused President Robert Mugabe's Zanu-PF party of trying to "hijack" a new biometric voter registration exercise that will see all would-be voters forced to register again before the 2018 polls.

Analysts have warned that many Zimbabweans may well not have the time or inclination to do so, especially if they live outside the country.

Mugabe has indicated he plans to stand again in the 2018 polls, apparently unwilling to acknowledge his all-too-evident frailty. He is 93 and has ruled Zimbabwe since independence in 1980. His party is bitterly divided as factions tussle for power in anticipation of his demise.

Tsvangirai meantime is coming under pressure to form a coalition with other opposition parties.

The MDC leader said: "I want to assure Zimbabweans that we will do everything we can to protect their vote, even though we cannot do it alone."