An American doctor climbing Everest when the devastating earthquake hit has described the heartbreaking moment her mountain guide died before her eyes , . Ellen Gallant , a cardiologist from Utah , was attempting to climb the world 's tallest mountain when the 7.8 magnitude earthquake struck , sparking an avalanche that killed 18 people . Four US citizens who were on Mount Everest are confirmed to have died along with 15 other climbers and Sherpas . There are believed to be up to 100 Americans still missing following the disaster on Saturday . Scroll down for video . American doctor Ellen Gallant was on Everest when the devastating earthquake struck . The tremors sparked a huge avalance killing 18 people , with Ms Gallant and another doctor desperately trying to save those injured . An experienced climber , Dr Gallant ( left ) had been training for 10 years to climb Everest . She helped tend to survivors and those gravely injured before rescue helicopters arrived to get people off the mountainside . Survivor Dr Gallant said she and an Indian doctor rushed to help the injured in difficult conditions following the avalanche , including the gravely-ill Sherpa , but said there was nothing they could do to save his life . ' I was outside , saw this huge blast coming down ' , she told ABC News . ' I ran into the tent , threw myself on the floor . When the vibration stopped , I went out and radioed over to the medical tent . 'They asked me and an Indian climber ( a doctor in the Indian army ) to take care of head injuries . 'We worked through the night , doing rounds , handing out medication , putting in IVs . 'Of the nine patients , one of them died last night — a 25-year-old Sherpa . His blood pressure had fallen . There was nothing we could do . ' Dr Gallant said they knew their lives were saved when they heard the sound of rescue helicopters landing on the mountainside , but now she is struggling to come to terms with what has happened . A critically injured person is carried on a stretcher out of Everest Base Camp following the avalanche . Dr Gallant said despite trying everything she watched a 25-year-old Sherpa die from his injuries on the mountain . The avalanche on Everest , pictured , killed 18 people including four Americans who were buried under the snow . Up to 100 US citizens are still missing following the disaster and at least 3,300 people were killed . Injured survivors from the avalanche waiting to be rescued . Dr Gallant said she is still dealing with the trauma of watching one young Sherpa died , saying : 'Now things have settled down , it 's hit me hard ' . 'Around 6am , we heard helicopters and we knew we would make it out of the woods . We were able to send the eight out , ' she said . 'When you go to medical school , you learn to focus on the task at hand . But now that things have settled down , it 's hit me hard . 'That young man who died in front of me — a 25-year-old should n't have to die . ' Among the mountaineers who died in the disaster is a 33-year-old Google executive Dan Fredinburg Marisa Eve Girawong , a New Jersey-born doctor based at the site , and Tom Taplin , filmmaker from Denver who was recording a documentary about the treacherous summit . Dan Fredinburg , left , and Marisa Eve Girawong , right , died in the avalanche in Everest on Saturday . Californian financial advisor Scott Holder was on Everest when the devastating avalanche killed 18 people . He described how he had to zip a dead body into a sleeping bag , and was giving medicine to the injured when a doctor told him : 'Don ’ t worry , you are just comforting these people . Most of them are not going to survive . ' Speaking to CNN , he said he felt lucky to be alive , having descended the mountain because he was suffering from a bad head cold . 'God definitely had his hand in my survival . My cold took me out of the danger zone . I guess you could say God gave me a cold . ' , he said . Read more here . They were buried by avalanches triggered by a huge earthquake in Nepal slammed into a section of the mountaineering base camp , where hundreds were preparing to make their summit attempts . The death toll across Nepal , China , India and Bangladesh has risen to 3,300 , with Nepalese officials speculating it could reach 10,000 . More than 6,000 have been injured across the region . It is the second time in two years Gallant has helped people hurt in an Everest avalanche . according to The Salt Lake Tribune . She and another doctor helped injured climbers at the mountain 's base camp medical tent after an avalanche struck In April 2014 , killing 16 people . Gallant spent more than 10 years training to climb the Himalayan mountain . She has previously climbed peaks on at least four continents during that period , including the highest mountain in Antarctica .
Dr Ellen Gallant battled to save the lives of those injured in avalanche . Spoke of her devastation seeing a 25-year-old Sherpa die in front of her . Earthquake sparked by devastating 7.8 magnitude earthquake in Utah . Four Americans among 18 people dead after huge avalanche on Everest .