The crisis in the Horn of Africa is a looming catastrophe. But it's a catastrophe the international community can avoid. If we learn lessons from the past and act fast, we can save hundreds of thousands of lives.

The United Nations estimates that this is the most severe food security challenge in Africa for 20 years. The extent of the crisis is daunting and the figures are so enormous that it is easy to forget that each number is a human life.

More than 11 million people are in need of urgent humanitarian assistance in Kenya, Somalia, Ethiopia and Djibouti. Unicef has labelled the situation in Somalia the "children's famine": reports say that two million young children across the Horn of Africa are malnourished and in need of immediate help.

There are more than half a million Somalis in the refugee camps, and 50,000 arrived last month alone – with nearly half of the children under five starving. They could be seen as the lucky ones as nearly 800,000 Somalis have fled their homes in search of safety.

They are mothers whose feet have been cut to ribbons after walking for weeks in search of safety for their families. They are children who have lost their brothers and sisters before help arrived. And they are parents who are forced to watch as their children starve to death, helpless to act.

The United Nations has declared a famine in two regions of southern Somalia, fuelled by a mix of violence, high food prices and drought. The British and Australian public, including staff at The Independent on Sunday who are donating a day's pay, have responded with incredible generosity.

Our governments are also providing considerable support to the people of the Horn of Africa as our two countries lead the world in quick and decisive action to make very clear that it is obscene that any child should starve to death.

Britain and Australia will help provide life-saving support, including food and water for almost four million people. This could relieve the most desperate suffering and buy some time before the next possible harvest this autumn. But the response from some wealthy, developed countries has been derisory and dangerously inadequate. It is shameful that there are European nations that have donated less than Sudan which, despite its relative poverty, is still doing what it can to help its neighbours.

The UN appeals are still underfunded by almost $1bn (£600m). Britain and Australia urge the rest of the world to join them to work to prevent this humanitarian disaster turning into a catastrophe on a scale of the 1984 Ethiopian famine.

The comparisons with Somalia are obvious. The international response back in the 1980s from both the public and their governments was eventually immense. But with the benefit of hindsight we know that it would have been more effective if the international community had acted sooner.

The warning signals were similar to those we are confronted with today. A drought in Ethiopia in 1981 was compounded by large-scale crop failure in 1984. Yet the Ethiopian civil war and the reluctance of Western governments to get involved, meant the full-scale international response was not fully organised until 1985. The human cost of late intervention was disastrous – the crisis was left largely unchecked in its early stages and eventually took a million lives.

Lessons have been learnt since then. We have early warning systems in place to ensure we are alert to these problems before there is a full-blown disaster across the Horn of Africa. This is about making sure food, water and medicines are in the right places, at the right times, to ensure people avoid starvation.

Second, we are working hard to ensure that countries are prepared for disasters before they hit. British and Australian aid programmes are targeting those most at risk in advance, making people less reliant on fragile crops, and communities more resilient as a whole. The scale of the crisis now would be much greater if it had not been for these preventive measures.

Third, we now have a better understanding of the importance of quick action to respond to a crisis. Emergency relief agencies are far better co-ordinated and can provide accurate data on the scope of the situation and funding needs.

But challenges remain, and are not restricted to the need for money. There are issues with delivering assistance: it is no coincidence that the worst-hit areas are among the most unstable and isolated. Nor are the interventions that are needed simple. Operations in Somalia are among the highest risk in the world.

Tragically, since 2008, a total of 14 UN World Food Programme relief workers have been killed there. The people hardest to reach are the ones most in need. If we are unable or unwilling to get into these regions, we will not be able to prevent a further escalation. That is why we channel our support through trusted partners – such as Unicef, and British and Australian charities and organisations – to get life-saving help to those who need it most. We do not engage with al-Shabab, but urge its people to stand by their commitment to allow humanitarian aid unhindered through to people in need.

In the longer term, we need to look at the systemic issues that are driving food insecurity across Africa and globally. The current situation is exceptionally severe – but not unique. The region has had six food crises in the past 30 years.

As important as humanitarian relief is, our aim is to get to a stage where it is no longer needed, as countries become less vulnerable to disasters. The world is now tackling food security, with the UK and Australia playing a leading role, investing in research and development.

We are investing in African businesses and supporting microfinance initiatives, and publicising the damage restrictive trade policies do to developing countries. The first G20 development ministers meeting in September will be an opportunity to develop practical measures.

The challenge before us is stark. The international community has the opportunity to save countless lives. But to do so our response needs to be rapid, flexible and mindful of past mistakes. We need to act now to avert an avoidable catastrophe.

Andrew Mitchell is International Development Secretary; Kevin Rudd is Australia's Foreign Minister