There were dancers, musicians, singers and flag-waving students – and, astonishingly, a break in the belts of rain that had been sweeping in across the sodden plains from the Matopo hills for days.

On the podium raised above a muddy school sports field in south-west Zimbabwe, Robert Gabriel Mugabe stepped up to the microphone. Wearing a white shirt, black tie, black cowboy hat and a jacket covered in his own portrait, Mugabe, in power since 1980, stood to thank his supporters for joining him to celebrate last week’s 93rd birthday which was, he said, “yet another chapter in my life”.

Yet if the tens of thousands of government supporters sent into Bulawayo city in the south-west of the former British colony to hear their leader speak were expecting his rousing rhetoric or trademark jokes, they were to be disappointed.

At the beginning of a sombre hour-long speech, delivered in a firm if halting voice, Mugabe described his life as “a long, long journey … a journey with its own joys [and] sorrows”, and spoke of his relatives who had died before him.

“When I look back I wonder why I have remained so long alone and alive. I cannot answer that, but I think sometimes I hear a silent voice saying … ‘each man, each woman, has a mission to fulfil in this world …’ I thank the Lord and say, I accept the mission,” Mugabe said to faint applause.

For loyalists, the dozens of marquees, attendance of hundreds of senior officials, multi-course feast and a vast 93kg birthday cake were barely adequate to mark the occasion. “We value our president’s birthday in a big way, just like many Christians value the birth of Jesus Christ,” Kudzi Chipang, Zanu-PF secretary for youth affairs, told NewsDay, a local newspaper.

Yet the veteran ruler, who in 2013 led his Zanu-PF party to an election victory amid widespread claims of vote-rigging, has given no indication that he will stand down before elections due next year. “You are saying I should stay, so we will be together,” said Mugabe during his speech on Saturday.

Observers say that, despite his increasingly evident frailty, Mugabe’s authority is intact. “There has clearly been some withering of his powers, but he remains the most authoritative figure, and both the party and the government wait on his decisions. He is still the boss, even if there is obviously a growing impatience … about what happens when he is gone,” said Dr Knox Chitiyo, an expert on Zimbabwe at the Chatham House thinktank in London.

There are two main contenders for succession, both on the stage on Saturday. One is Mugabe’s wife, Grace, who has a reputation for extravagance and fierce verbal attacks on rivals. Earlier this month Grace, 51, promised that she would push Mugabe in a wheelchair if needed, so he could campaign in the coming presidential polls, and suggested that Mugabe could be elected even if “nature claimed him” before the polls.

The president last week described his wife as “a very strong character” who was “very much accepted by the people”. On Saturday she told the crowd that Zimbabwe was “blessed to have Comrade Robert Mugabe as the leader of our country and the leader of our revolutionary party”.

Her rival is the vice-president, Emmerson Mnangagwa. Earlier this year Mnangagwa, 70, posted a picture of himself with a mug bearing the slogan “I’m the Boss”, prompting speculation that he was preparing a bid to oust the president or had already been tipped for the top post. However, opponents of Mnangagwa, a veteran of the bush war which brought Mugabe to power, say he would not have sufficient legitimacy to either quell dissent or rehabilitate the nation on the world stage.

While the rivals squabble, pressure is building. Though many in Africa laud Mugabe as a nationalist who battled once against colonialism and now against “neo-imperialist” western powers, others blame him for destroying the economy of a country once known as the “breadbasket of Africa”.

A series of controversial measures over the past 20 years have caused massive disruption. In 2009 hyperinflation forced Zimbabwe to adopt foreign currencies – largely the US dollar – after its own collapsed. A controversial bond note backed by loaned money has staved off total economic disintegration, but clinics are now without drugs, banks short of cash, roads go unmaintained, there are few jobs, police systematically extort cash from travellers, and hunger threatens millions.

One result is a wave of unrest. Local observers said there were more demonstrations across the country in 2016 than in any other year since Zimbabwe won independence.

The protests brought together different interest groups. Some were middle-class officials once loyal to the government but angered by repeatedly delayed salary payments. Others were young demonstrators organised largely through social media and led by a new generation of activists. Officials have described the protesters as “terrorists” and blame foreign powers for sabotaging the economy and stirring unrest.

Groups monitoring human rights abuses documented more than 700 incidents of political violence in 2016, and another 50 so far this year.

These included abductions by the military and police, who broke into the homes of opposition activists. Many were then held and tortured. Spouses and children were assaulted if the targeted victims could not be found.

One leader is Patson Dzamara, 30, whose brother was abducted almost exactly two years ago. “The security agencies have been very heavy-handed. I’ve been abducted, beaten up, lost two cars, and I have to go to court almost every week to face trumped-up charges. That is why the momentum of our [protest] movement has been inhibited,” said Dzamara.

But the new wave of activists is yet to join forces effectively with established older organisations, such as the Movement for Democratic Change (MDC), the only opposition party with national reach. The MDC is fractured and, despite tortuous talks which continue, has been unable to conclude a deal with the myriad smaller actors who could play a vital role.

“The aspect of unity is very critical … The opposition and the social movement is suffering from Zanu-PF’s divide and rule strategy,” said Dzamara.

Experts say the 2018 elections will thus be fought by coalitions – an internal alliance within the Zanu-PF which may temporarily obscure the rivalries within the party, and an inter-party alliance among the opposition.

“Zimbabwe is now in elections mode. We are in the runup to 2018 [polls] and there is a lot at stake for all the players,” said Chitiyo.