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 shouldn'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 Nepal .
Four Americans among 18 people dead after huge avalanche on Everest .