The townships of suburban Harare once boasted water and sewage systems that were the envy of Africa. They are now as broken as Zimbabwe itself. Raw sewage spills from manhole covers and is pumped into the city's main reservoir. Thousands depend on the generosity of “water samaritans” lucky enough to have their own boreholes. Where even the poorest had taps and toilets of their own, people are queueing up at hand pumps, one engineer laments. “Civilisation has gone in reverse.”

People are also dying. A cholera outbreak that has killed more than 500 people could infect 60,000 by March, according to Oxfam. The outbreak is spreading four times faster than usual for want of transport to take victims to hospital, and basic medicines for those who get there. To contain the epidemic the Health Minister has advised Zimbabweans to stop shaking hands, but it has already spread to South Africa.

In Zimbabwe's rural hinterland five million people will soon need food aid that the World Food Programme cannot afford to distribute. The Government is powerless to count the number dying of hunger, much less hand out food itself. But aid workers have seen children foraging in rubbish dumps alongside wild animals, and in Matabeleland one story encapsulates the despair of a nation - the story of a woman who, unable to feed her children, fed them and herself a fruit that she knew was poisonous. They were buried together.

Such are the tragedies that lend meaning to Zimbabwe's statistics; to its 90 per cent unemployment, its 230 million per cent inflation and its average life expectancy of barely 40 years. In 1990, Zimbabweans could expect to live to 63.

Nine months ago, Robert Mugabe was rightly excoriated for stealing a presidential election having destroyed his country's economy and brutalised its Opposition. Survivors clung to the notion that things could not get worse. They were wrong. As disease and famine take hold, the army has been condemned even in state-controlled newspapers for brazen looting. Morgan Tsvangirai, the opposition leader, has concluded more in bewilderment than anger that “everything seems to be collapsing around us”.

The news from Zimbabwe can seem woefully familiar. This is, indeed, an incremental catastrophe, eclipsed as an international priority by the financial crisis. But it is real and preventable. Mr Mugabe could have triggered the release of US and British aid worth £1 billion, and billions more in investment, by ceding just one significant ministry to Mr Tsvangirai. He has chosen not to.

Zimbabwe's neighbours cannot simply stand by. Nor can the United Nations Security Council, which failed to pass a new resolution on Zimbabwe in July because of an unconscionable and self-defeating Russian veto. If international intervention on humanitarian grounds is justified in Darfur and Congo, it is manifestly justified in Zimbabwe.

President Bush has six weeks left to shape his legacy. Barack Obama has unprecedented moral authority in the continent where his father was born. Jacob Zuma, the front-runner to become South Africa's next president, is no Mugabe loyalist. Between them they can and must secure a mandate to help to end Zimbabwe's nightmare - not after Mr Obama's inauguration, but now.