Issak Abed Rabbo and his family in Gaza City have had no electricity for four days straight. They have long since exhausted their supply of cooking gas and are forced to rely on an old-fashioned waboor or kerosene cooker. Abed Rabbo and some 30 family members in his home are lucky to have food, he says, but he knows of others who do not have enough to eat. "Gaza has gone backward 50 years," he said grimly on Sunday morning, hours after Israeli forces launched the ground offensive of their nine-day old military operation in the Gaza Strip. "We have food, but there is no electricity, no transportationâ€¦no gas." But it is the frequent shelling from Israeli tanks and planes that he and his family are concerned about the most. Abed Rabbo said his children and grandchildren were particularly scared on Sunday night after hearing thunderous explosions of war. "We didn't sleep last night," said Abed Rabbo, vice president of the Retired Civil Servants Society in the Gaza Strip. "We didn't sleep at all. The children were screaming at each explosion. Everyone was in one room screaming." In the Southern Gaza Strip near Khan Yunis, Dr. Abdullatif el-Haj, acting director of the European Gaza Hospital, said Sunday morning that his hospital had been completely dependent on a generator for electricity for the last 16 hours. If anything were to happen to the generator or their back-up one, which is less efficient, all the machines in the hospital would stop working, including respirators and ventilators. "The patients who are in the intensive care unit would die... because they depend on these machines," he said. The hospital was also facing a deficiency in some medicines, such as certain strong antibiotics and drugs for critical care patients, he said. While they had not run out completely, they were at risk of running out in the coming days, he said. Meanwhile, about 20 members of the hospital's staff had not arrived on Sunday morning, because of roads blocked due to the military operation. He said they were trying to bring them in ambulances to the hospital. The staff had also collected food for the hospital's employees - which number 800 - and patients for the next week or two in case they are cut off from the rest of the Strip. But Haj was most concerned about the possibility that their hospital could be overrun by a new influx of patients in need. "I would be in a very bad situation regarding a shortage of ventilators, operating rooms and exhausting our staff," he said. Gaza's civilians cowered inside as battles raged, while terrified residents in other areas fled in fear. In the southern town of Rafah, one man loaded a donkey cart with mattresses and blankets preparing to flee. Lubna Karam, 28, said she and the other nine members of her family spent the night huddled in the hallway of their Gaza City home. The windows of the house were blown out days earlier in an Israeli air strike, and the family has been without electricity for a week, surviving without heat and eating cold food. She said no one slept overnight. "We keep hearing the sounds of airplanes and we don't know if we'll live until tomorrow or not," she said. Gaza health officials said the dead included a 12-year-old girl, five members of a single family, eight civilians killed by a tank shell in the northern Gaza town of Beit Lahiya and an ambulance driver. The new deaths brought the death toll in the Gaza Strip since last Saturday to more than 500. Palestinian and UN officials say at least 100 civilians are among the dead. Meanwhile, United Nations Relief and Works Agency (UNRWA) officials said on Sunday that contrary to statements made by Israeli officials, there is a humanitarian crisis in the Gaza Strip. "Bread and wheat are going to run out extremely rapidly, and people are going to start getting extremely hungry," said UNRWA spokesman Chris Gunness. "Medical supplies are in critically short supply. When you have a situation where houses are being blown up and women and children are being maimed, I would say that's a humanitarian crisis." Top Israeli government officials have declared in recent days that there is no humanitarian crisis in Gaza, and that Israel would not allow one to occur. AP contributed to this report.