Ban Ki Moon has warned the international community that Pakistan is facing a "slow-motion tsunami" of destruction. The UN Secretary-General urged the world's richest countries to give more aid to the flood-ravaged country at a special General Assembly meeting in New York. He said up to 20 million people are urgently in need of assistance and 160,000 square kilometres of land is under water - an area larger than more than half the countries of the world. The Government has announced it will double aid to disaster-hit Pakistan. International Development Secretary Andrew Mitchell said an extra £33 million is being offered on top of the £31.3 million already pledged to help cope with the effects of floods. Speaking in New York, Mr Mitchell told the UN General Assembly it was "unacceptable" that the international community had not done more, and urged other donors to step up their efforts. Mr Mitchell visited Pakistan on Wednesday before flying to New York to lobby the international community to do more to alleviate the humanitarian disaster. He said: "It is clear that unless more aid is delivered now, many more people will die from disease and malnutrition. It is deeply depressing that the international community is only now waking up to the true scale of this disaster. The UK is already helping more than three million people in flood-affected areas." US Secretary of State Hillary Clinton pledged a further $60 million, taking the total American contribution to $150 million.