Islamabad , Pakistan ( CNN ) -- A second wave of floodwater is expected to wash through southern Pakistan this weekend , adding hundreds of thousands of people to the number already stranded by a first wave earlier this month , Pakistani officials said . At least 1,384 people have died and another 1,630 have been injured by flooding that has damaged or destroyed 8,300 Pakistani villages so far , according to National Disaster Management Authority spokesman Ahmed Kamal . The United Nations said it was racing against time to reach the suffering . `` Relief supplies must reach women , men and children as soon as possible , in order to avoid further death caused by waterborne diseases and food shortages , '' said Martin Mogwanja , the United Nations ' humanitarian coordinator for Pakistan . `` The death toll has so far been relatively low compared to other major natural disasters , and we want to keep it that way , '' he said . Two of 19 military helicopters pledged by the United States arrived in Islamabad , Pakistan , on Thursday to help in the humanitarian relief efforts , a U.S. Embassy spokesman said . These aircraft replace six U.S. Army helicopters that will return to duty in Afghanistan , the embassy spokesman said . The Army helicopters rescued more than 3,000 people and delivered relief supplies since arriving in Pakistan on August 5 , the spokesman said . Farther north , more than 100 U.S. troops are on the ground in the volatile Swat valley , helping the Pakistani government deliver supplies and rescue people from flood-ravaged areas . None have yet encountered Taliban fighters . `` Obviously there 's a militant threat in this region , but the Pakistani military has done an incredibly committed job -- providing us multiple layers of security around our units , '' said U.S. Army Brig . Gen. Michael Nagata in a conference call from Pakistan . `` All our activities and helicopters are completely safe . '' The bigger problem , said Nagata , is the weather . In the last two weeks , air crews have only been able to fly five days because of the relentless monsoon rains . The initial wave of the flooding came after torrential rains two weeks ago filled rivers in northern Pakistan that swept southward . Weather experts said a year 's worth of rain fell in a day at the peak of the relentless downpours . A second wave of floodwater from rain that fell in northern and central Pakistan the next week is now reaching the Sindh province in southern Pakistan , according to CNN meteorologist Brandon Miller . An apparent bottleneck of water from the first flood wave at the Sukkar dam could be overtaken by the second wave , Miller said . `` This could lead to a situation where the two flood waves could build upon each other and lead to even more catastrophic flooding , '' Miller said . Pakistan emergency officials predicted the second wave could reach Sukkar on Saturday evening . Hundreds of thousands of people living along the Indus River in northern Sindh could be stranded along with the tens of thousands stranded by the first wave , said Pakistani Navy Lt . Commander Jawad Khawaja . Many residents have ignored government warnings to evacuate the area , causing a big concern , Khawaja said . More than 14 million Pakistanis are affected , with 400,000 rescued from floodwaters , the government said . It estimated that 723,950 homes have been damaged or destroyed . In the mountainous north , water funneled down treacherous slopes , quickly engulfing the roads below . It surged down the Indus River , spreading economic , political and social woes through the heart of Pakistan . The smell of bodies filled the air in many places , where mere seconds of unstoppable water ended lives . Many witnesses , even those who thought they had seen everything in this land marred by crisis and killing , said they were stunned by the suffering wrought by the monsoons . U.S. President Barack Obama , in a statement marking the 63rd anniversary of Pakistan 's independence on Friday , said , `` We will remain committed to helping Pakistan and will work side by side with you and the international community toward a recovery that brings back the dynamic vitality of your nation . '' CNN 's Chris Lawrence and Samson Desta contributed to this report .
Officials fear hundreds of thousands more could be stranded . Many residents are ignoring warnings to evacuate area . More flooding is expected this weekend , Pakistani official says . Promised U.S. military helicopters start to arrive .