Surrounded by his grandchildren, Mahmud al-Sarsawi Sunday lay on a table in a corridor hooked up to an oxygen tube in a school-turned-bomb-shelter in the besieged Gaza Strip.
"We all came here to escape the Israeli airstrikes," said the elderly man from the Shujaiyya neighbourhood, adding he was among about 70 people sheltering in the building for the second day from Israeli air strikes.
"The situation was terrifying, and we had no choice but to seek refuge," added Sarsawi, 68, who is worried he may run out of oxygen.
He had taken cover in one of 44 schools run by the United Nations Relief and Works Agency for Palestine refugees (UNRWA), which they have opened up as shelters.
More than 20,000 people in the Palestinian territory have been displaced due to fighting, UNWRA says, after Hamas militants launched thousands of rockets, and stormed into Israel before dawn on Saturday in a series of devastating attacks on southern Israeli towns.
Retaliation was swift from Israeli forces, who launched air raids on the impoverished and densely-populated Gaza Strip, where 2.3 million people live crammed into a small piece of land.
"I'm telling the people of Gaza: get out of there now, because we're about to act everywhere with all our force," Israeli Prime Minister Benjamin Netanyahu warned late Saturday, telling people to leave certain areas saying Hamas hideouts in Gaza would be reduced to rubble.
In just two days, about 600 people have been killed in Israel and at least 370 people in Gaza, according to figures from officials on both sides.
Inside the classroom, women members of Sarsawi's family sat on sponge mattresses brought from their home, surrounded by cooking gas, canned food and jumbled bags of clothes.
Amal Al-Sarsawi, 37, said they were still in shock, after hearing rockets thudding into Gaza. "We gathered what we needed from the house and rushed to the school," said the mother-of-five.
She says they couldn't sleep all night, as they tried to calm their frightened children.
"The situation is unbearable psychologically and economically," she said.
A Hamas government spokesman said 13 towers and residential buildings had been destroyed, with 159 single residential units gone. Another 1,210 apartments were partially damaged.
An UNRWA employee, who asked not to be named, told AFP the New Gaza Boys School, where the Sarsawi family is sheltering, could house at least 300 people -- with three families to each classroom.
Children kicked around a deflated football in the school's courtyard, while women sought to create screens from clothes to have some limited privacy.
In one of the hallways, one woman who fled with 14 relatives from the north sat with her head in her hands. Unable to hold back tears, she said they couldn't afford milk to feed two small babies.
"We haven't eaten anything since yesterday morning. We barely escaped from home with some clothes," she said.
The UN's World Food Programme said Sunday it was "deeply concerned" about the impact of war on civilians struggling to get essential food supplies.
"While most shops in the affected areas in Palestine currently maintain one month of food stocks, these risk being depleted swiftly as people buy up food in fear of a prolonged conflict," it said in a statement.
Hundreds lined up Sunday in front of bakers to get bread as the sound of explosions rang out around them.
"I am hosting more than 20 people, relatives, and friends who came from border areas," said one man holding up five loaves of bread.
Leila Saqr, who lives in one of the areas singled out by the Israeli army, spent the night with her family and three children in the entrance to her building.
"My children were scared. They screamed all night," she said.
