Robert Mugabe marked his 85th birthday yesterday with a sumptuous banquet in Harare at the start of a week of parties which observers say is a further sign of the Zimbabwean president's defiance in the face of growing criticism of his regime.

His latest show of excess came as prime minister Morgan Tsvangirai said "maybe US$5bn (£ 3.5bn)" would be needed to rehabilitate the collapsed health, social and education systems.

Surreal celebrations got under way on Friday as schoolboy pipers, accompanied by drum majorettes, marched through the decrepit capital and members of a ruling party youth organisation sold $10 raffle tickets.

Teetotal Mugabe's private party yesterday was hosted by his wife, Grace, 44, and attended by friends and a number of African diplomats. But state television did not, as is customary, broadcast his speech.

A $100-a-ticket gala dinner at Harare's Rainbow Towers Hotel on Wednesday is advertised as a musical extravaganza including Nigerian hip-hop star 2Face, Congolese rhumba band Werrason and a host of local acts. The parties will culminate on Saturday with a public feast and concert at Chinhoyi, about 50 miles west of Harare, which is to be televised. Dozens of animals will be slaughtered for the event and guests include hundreds of children also born on 21 February.

Zimbabwe University political science professor John Makumbe said the birthday display was the latest of many signals that the ruling Zimbabwe African National Union Patriotic Front (Zanu-PF) does not intend to respect the power-sharing agreement that saw Tsvangirai sworn in on 11 February.

"The money for the parties and the cattle and chickens donated are extracted from people virtually against their will," he said. "Thousands have died from cholera and many students are not attending school or university because teachers are not paid. It's unbelievable that he can blow quadrillions of Zimbabwe dollars on parties."

The celebrations have been organised since 1986 by a Zanu-PF youth group called the 21 February Movement. Initially modelled on scouting and aimed at promoting children's rights, it has increasingly become a young sycophants' association.

Zanu-PF youth leader Absolom Sikhosana defended the Chinhoyi event: "It is not a feast per se, but an event where youths have a chance to meet their hero. This inspires them to emulate his exemplary qualities of nation-building, patriotism and principled leadership."

In a sign of the times, the 21 February Movement set out to raise only $500,000 (£350,000) for Mugabe's birthday week against a reported $1.2m last year. Last week Sikhosana made a heartfelt plea on national radio for benefactors to make good on their promises: "We know things are tough, but it would be nice to honour the pledges you made."

According to some reports, pledges for only £70,000 have come in, much in the form of food donations. State media has reported that each district in Zimbabwe is expected to donate 50 cattle and to raise US$1,500 (£1,000).

Mugabe had already run roughshod over the power-sharing agreement by appointing 61 ministers instead of the agreed 31, Makumbe said. "Each will need their Mercedes, their 4x4, their driver, bodyguard and housing. At the same time, Tsvangirai is trying to raise money for basic reconstruction."

Amid scepticism from the international community, Tsvangirai and South African President Kgalema Motlanthe did their best to indicate progress on Friday. At a joint press conference in Cape Town, Motlanthe even claimed that the cholera crisis, which the UN says has killed 3,800 people and is worsening, had been "contained".

Tsvangirai played down the plight of his deputy agriculture minister, Roy Bennett, and 30 other activists who are in jail for alleged plotting against the regime. He said: "We are working slowly to deal with that matter and to make sure it does not become the focus of the attention. The real attention has to be on the plight of Zimbabweans."

The two men announced that Southern African finance ministers are this week expected to announce a $1.5bn loan to Zimbabwe, to be underwritten by the African Development Bank. The institution is part-funded by Europe and the US, but decision-making rests with African governments.

International donors remain concerned that aid will be diverted to the ruling party, just as £20m from South Africa last December mostly ended up in the hands of party supporters.