Zimbabwe's Tourism Minister has backed President Robert Mugabe, 93, who was endorsed by his Zanu-PF party as the presidential candidate for elections in 2018.

The oldest head of state has made regular trips to Singapore for "scheduled medical reviews", according to his spokesman George Charamba, but these trips 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 last month.

Speaking to BBC's Hardtalk programme, Tourism Minister Walter Mzembi backed Mugabe 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".

"They have already indicated at the last national conference that they want him to stay on, it's not really about the statistic but what he is offering, his leadership. I want him to stay on," he said.

Questioned about Mugabe's ability to rule over the country of over 16 million, Mzembi said the head of state's "faculties are completely in place".

"I have just parted ways with him recently from Ghana (where Mugabe was attending 60th Independence celebrations earlier this month), and I was able to watch him in action. You wouldn't imagine that he is 93 – it's just a statistic really."

The Minister added: "He is completely of sound mental state and completely in charge of his faculties".

Robert Mugabe birthday
21 February 2017: Zimbabwe's President Robert Mugabe reads a card during his 93rd birthday celebrations in HararePhilimon Bulawayo/Reuters

Dismissing rumours that Mugabe was in bad shape when he was flown to Singapore for medical treatment, Mzembi explained how the nonagenarian had "immediately proceeded to Ghana, paying testimony to how physically fir he is."

The race to succeed Mugabe took a peculiar turn last month when his wife, Grace Mugabe, reportedly offered to field her husband's corpse as an election candidate to demonstrate Zimbabweans' affection for him. Commenting on the First Lady's remark, Mzembi said the "metaphor" was used in reference to the fact that "the ideologies of (dead people) are basically how we govern, how we function today".

"With philosophers like Jesus Christ, Socrates, Muhammad and many of them, they have philosophies that continue to govern us even when they lay in state, in their graves. It's about the philosophy of a leader."

In September last year, neighbouring Botswana President Ian Khama said his counterpart should step aside without delay, saying: "Without doubt. He should have done it years ago." In his remark that breached an African diplomatic taboo prohibiting criticism of fellow leaders, Khama warned Mugabe could not provide the leadership to pull Zimbabwe out of its biggest financial and economic crisis since 2009.