Islamabad , Pakistan ( CNN ) -- Flooding has displaced an additional 1 million people in Pakistan 's Sindh province in the past two days , according to new U.N. estimates released Friday . `` We have more people on the move , to whom we need to provide relief . An already colossal disaster is getting worse and requiring an even more colossal response , '' said Maurizio Giuliano , a spokesman for the U.N. 's Office for the Coordination of Humanitarian Affairs . Giuliano said rains have forced the evacuation of an estimated 1 million people in southern Sindh in the past 48 hours or so . `` The magnitude of this crisis is reaching levels that are even beyond our initial fears , which were already leaning towards what we thought would be the worst . The number of those affected and those in need of assistance from us are bound to keep rising . The floods seem determined to outrun our response , '' he said . The U.N. also said Friday that it is increasingly concerned about flood-driven malnutrition among children . `` The flooding has surrounded millions of children with contaminated water , '' said Karen Allen , deputy representative of the United Nations Children 's Fund ( UNICEF ) in Pakistan . `` Most have nothing else to drink . We fear the deadly synergy of waterborne diseases , including diarrhea , dehydration and malnutrition . '' Acute malnutrition was high in much of Pakistan even before the floods . For instance , 27 percent of children under 5 in Baluchistan province were malnourished , as were 17 percent of children in Punjab , according to the U.N. A hospital in Sindh is overrun with people suffering from waterborne illness ; two children share each bed and more are on the floor . A doctor at the hospital said there are `` not enough resources because of huge population ... coming to this hospital . '' Remat Chacher , a farmer in Sindh , escaped the floodwaters with his wife and two children earlier this month . But then his 3-month-old daughter Benazir got sick . `` She started to get fever and could n't keep anything down ... lots of belly pain , '' said Ulla , the infant 's mom . A few days later , the same symptoms struck the Chachers ' son , 2-year-old Wazira . Both children died on the way to the hospital , with Wazira weighing just 8 pounds and Benazir weighing 2 pounds . Floodwaters have started to recede across Pakistan , but in the Indus delta , the potential for more flooding remained high , especially given high tides in the Arabian Sea , where the Indus spills out . Already , more than 17 million Pakistanis -- from the Chinese border in the north to the mouth of the Indus in the south -- have been affected by the monsoon floods that began a month ago . To date , Pakistan 's unfolding tragedy has claimed 1,600 lives , according to the National Disaster Management Authority . That number is likely to rise as more drowned bodies are discovered in receding waters . Many refugees have sought shelter at relief camps , where food and drinking water are now available . But every day , there are new camp arrivals -- people who were already poor , who now have nothing . Along the flooded Swat River in northeastern Pakistan , six local aid workers have spent two weeks braving the torrents on rafts they built from used tire tubes , bamboo and gaffers ' tape after motorized boats failed to arrive . The workers are ferrying tents , blankets and other supplies to hundreds of thousands of people stranded across the river and cut off from normal supply routes . Last year , bombs and bullets from the army 's offensive against the Taliban destroyed many homes and lives in the region . Residents had barely begun to recover when the rains came . `` We are fed up , '' said Shahravan , a 65-year old man who lost his house in the floods . `` You do n't ask a dead man why he 's in his grave . It 's not his choice . '' Fayas Muhammad , another local , said he lost his leg when his house was mistakenly bombed in last year 's fighting . The same blast took his wife and son . `` We are very sad for all that Swat has been through , '' he said . The damage from Pakistan 's worst humanitarian catastrophe is sure to hurtle the impoverished nation back in terms of development . This week , America 's top aid official saw firsthand the dire needs in Pakistan . Dr. Rajiv Shah , administrator for the U.S. Agency for International Development , said he was deeply moved by his visit to Sukkur and that aid agencies were `` scaling up their response efforts as quickly as they possibly can . '' Shah announced the United States would be diverting another $ 50 million for flood relief from the Kerry-Lugar Act , which allocated $ 7.5 billion in nonmilitary assistance to Pakistan over five years . CNN 's Sanjay Gupta , Reza Sayah , Samson Desta , Sara Sidner , Moni Basu and journalist Nasir Habib contributed to this report .
NEW : U.N. is increasingly worried about flood - related malnutrition among children . An official says a ` ` colossal disaster is getting worse '' About one million additional people have been displaced in Sindh ' , the U.N. says . They have ordered evacuation in the Indus River delta .