Zimbabwean opposition parties have said they would not allow President Robert Mugabe, to "lead the country from a wheelchair", as the 2018 general election draw nearer.

Mugabe, 93 was endorsed by his Zanu-PF party as the presidential candidate for elections in 2018, but the oldest head of state's regular trips to Asia for "scheduled medical reviews" systematically fuel rumours he had been taken gravely ill or may even have died.

Mugabe, who came to power after independence from Britain in 1980, appeared frail and mumbled several times as he delivered a speech during one of his birthday celebrations in February.

Opposition leaders on 5 April said they would not be stopped by a "wheelchair-bound" Mugabe, and that they would call for massive street protests to call on Zimbabwe's electoral body to implement electoral reforms are implemented to ensure free and fair elections ahead of the vote.

A official of the opposition MDC-T party, Elias Mudzuri, told crowds at a rally in downtown Harare on Wednesday that the President is now too old to govern the country, which is facing its worst financial crisis in almost a decade with a shrinking economy combined with an estimated 80% unemployment rate and the worst drought in 35 years. In February, the US will handed an additional $4m (£3.2m) in aid for fighting famine in the southern African nation.

"Mugabe has put a wall between the people and their food and we cannot be defeated by one person. If you go to banks there is no money and pensioners are not getting their dues yet some people think that we can allow Mugabe to rule us from a wheelchair," Mudzuri said.

"We must be united against Mugabe and we are not going to allow Mugabe to get older and continue to rule us from a wheelchair; No, it's enough."

Mudzuri was attending a meeting organised by the National Electoral Reform Agenda (Nera).

The opposition coalition, which represents some 18 political parties including political heavyweight Joice Mujuru's Zimbabwe People First (ZPF), is demanding reforms before next year's polls, and the return of the United Nations Development Programme (UNDP) in an oversight role to ensure the credibility of the election.

Despite growing calls for Mugabe to step down and nominate a successor, Tourism Minister Walter Mzembi last month backed the nonagenarian as the ruling party's candidate, saying the President should run for the elections "as long as the people ask him to carry on, as is the case now".