Nearly half the $459 million (295.8 million pounds) needed for initial relief in Pakistan's worst ever floods has been secured after days of lobbying donors and warnings that the country faces a spiralling humanitarian catastrophe, the United Nations said on Wednesday. But despite the fresh funds, only a fraction of the six million Pakistanis desperate for food and clean water have received help after the worst floods in decades killed up to 1,600 people and left two million homeless. "There has been an improvement in funding. Donors are realising the scale of the disaster," U.N. spokesman Maurizio Giuliano told Reuters. "But the challenges are absolutely massive and the floods are not over." "The size of (the area affected by) this disaster is equivalent to Austria, Switzerland and Belgium combined. That's pretty scary." A few days ago, only a quarter of aid pledged had been received, prompting U.N. Secretary-General Ban Ki-moon on a visit to Pakistan to urge foreign donors to speed up funding and avert more deaths. So far, food rations and access to clean water have only been provided to around 700,000 flood survivors, the U.N said. The damage and cost of recovery could shave more than one percentage point off economic growth, analysts say. Pakistan's High Commissioner to Britain, Wajid Shamsul Hasan, said the cost of rebuilding could reach up to $15 billion. Victims are relying mostly on the military, the most powerful institution in Pakistan, and foreign aid agencies for help. Nevertheless, a military coup is considered unlikely. The army's priority is fighting Taliban insurgents, and seizing power during a disaster would make no sense, analysts say. Hundreds of villages are isolated, highways and bridges have been cut in half by floods and hundreds of thousands of cattle -- the livelihoods of many villagers -- have drowned. The United Nations has warned that up to 3.5 million children could be in danger of contracting deadly diseases carried through contaminated water and insects in a crisis that has disrupted the lives of at least a tenth of Pakistan's 170 million people. U.N. Food and Agriculture Organisation says Pakistan could face food shortages if its farmers miss the sowing season which is due to start next month. Public anger has grown in the two weeks of floods, highlighting potential political troubles for President Asif Ali Zardari's unpopular government which is a major U.S. ally in the war against Islamist militancy. Some Pakistani flood victims blocked highways to demand government help and villagers clashed with baton-wielding police on Tuesday after opposition leader Nawaz Sharif tried to distribute relief in Sindh.