Gordon Brown has called on the international community to tell Zimbabwean President Robert Mugabe "enough is enough".
With the beleaguered African state now in the grip of a cholera epidemic, the Prime Minister said in a statement that the situation had deteriorated to the point where it demanded an international response.
He said: "This is now an international rather than a national emergency. International because disease crosses borders. International because the systems of government in Zimbabwe are now broken. There is no state capable or willing of protecting its people.
"International because - not least in the week of the 60th anniversary of the universal declaration of human rights - we must stand together to defend human rights and democracy, to say firmly to Mugabe that enough is enough."
Mr Brown said the immediate priority was to prevent more deaths through the distribution of re hydration and testing packs.
He called for the establishment of a "command and control structure" in the capital, Harare, to co-ordinate the work of donors and NGOs to ensure that international aid reached the people who needed it most.
At the same time, Mr Brown said that he had been in close contact with African leaders to press for stronger action "to give the Zimbabwean people the government they deserve".
He said that he now hoped that the United Nations Security Council would meet urgently to consider the situation in Zimbabwe.
"The people of Zimbabwe voted for a better future. It is our duty to support that aspiration," he said.
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