TEL AVIV, ISRAEL, and LONDON -- "I think Gazans' worst fear at the moment is the sun setting."

Nour Alsaqa, a 23-year-old from Gaza City, along with the 2.3 million people living in the Gaza Strip, is now living under siege.

"Because once the sun sets and the night comes... [the] bombings don't stop," she told ABC News. "And not only don't they stop, they happen everywhere at once... The house shakes, the windows crack, the doors bang... Everything is just so intense and it feels like the world is ending for a few minutes here and there."

In response to the surprise attack on Israeli soil by Hamas, which has killed at least 900 Israelis, Gaza has been subjected to a relentless barrage of strikes from the Israeli air forces. Since Saturday, the Israel Defense Forces claims that 1,500 military targets have been struck and several senior Hamas figures have been killed.

But in one of the world's most densely populated areas, the impact of the strikes on the civilian population has already been devastating, just as it was in the recent conflict between Hamas and Israel in 2021. However, the death toll has already far surpassed that of the 10-day war. So far, at least 900 people have been killed -- including at least 260 children and 230 women -- and another 4,500 have been wounded in Gaza since Saturday, Palestinian authorities said. The death toll is expected to rise significantly as the bombardment continues.

"I sometimes managed to get a few videos here and there," Alsaqa said. "But even the videos, when I watch them later on, they do not showcase a bit of how horrific experiencing a building being bombed right across the street is."

Videos of the destruction wrought by the bombardments show a harrowing picture, with high-rise buildings flattened, streets destroyed and Gazans searching through the rubble for their loved ones. In one strike in the south of the Gaza Strip, a man said he had lost 19 family members after their house was struck, according to The Associated Press.

Israel's defense minister, Yoav Gallant, has ordered a "complete siege" of Gaza -- which has been blockaded by Israel since the militant group Hamas was elected in 2007 -- promising to cut off supplies of water, fuel and electricity, which could have dire humanitarian consequences. "All the places that Hamas hides in, operates from, we will turn them into ruins," Israeli Prime Minister Benjamin Netanyahu said, telling the people of Gaza to "get out of there now" on Saturday night.

But under full blockade on the Israeli side, and the Egyptian border sealed off, there is nowhere for the population to go.

For the time being, Alsaqa and her family still have access to water, but are rationing their use of electricity and food supplies. With very few local businesses still operating to provide food and basic necessities, they rely on the help of a neighbor.

The World Health Organization, Médecins Sans Frontières/Doctors Without Borders and other aid agencies are calling for a humanitarian corridor.

"The health system is running beyond its capacity, given the number of injured," Tarik Jasarevic, WHO spokesperson, said. The WHO has also documented 37 attacks on health care facilities, with six health workers killed, according to their latest report.

"The intensity of the bombardments by the Israeli army in Gaza is making movement almost impossible and preventing us from getting an overview of the consequences for the population," an MSF spokesperson in New York told ABC News. "However, what we are seeing are hospitals overwhelmed by the number of wounded, surgical units running day and night, and tens of thousands of displaced people."

"Medicines come through two main points, the Rafah crossing [between Egypt and the Gaza Strip] is one of them, it was bombed this morning," Dr. Khamis Elessi, a neurorehabilitation and pain medicine consultant, told ABC News. "The other is already closed by [the] Israeli government. So now there is no way of bringing medicine into Gaza. The situation is getting worse by the day."

Stocks of drugs available for doctors were running empty, he said, and the destruction on the streets has quadrupled the time it takes for victims to get to the hospital.

"It's killing them slowly here, by removing electricity power water... every aspect of life is affected," he said. "If you look through the window, you cannot see the sun at the moment, you can only see the every aspect of life is affected. If you look through the window, you cannot see the sun shining at the morning, you can only see the dark and suffocating clouds of the bombing."

And the war between Israel and Hamas has only just started.

As part of "Swords of Iron" -- the code name given to Israel's military response -- 360,000 Israeli reservists have been called up. The significant buildup of military equipment on the border has led to fears that Israel may launch a ground invasion.

According to the IDF, all of the towns taken by Hamas militants have now been liberated, but a significant military presence built up at the border and Netanyahu's vow to "exact a price" that will be "remembered for decades to come" has added to fears of a ground incursion into Gaza.

Such an operation could pose a risk to the lives of those kidnapped to the Gaza Strip following Hamas' attack. Hamas has said it will begin executing Israeli hostages -- which are believed to number at least 100 -- if the bombardment continues. And the Hezbollah militant group in Lebanon, backed by Iran, has promised to invade Israel from the north if a ground invasion of the Gaza Strip is carried out by Israeli forces.

Only a few days in, analysts have warned that there are very real fears the war could escalate further into a regional conflict.

ABC News' Nasser Atta and Ibtissem Guenfoud contributed to this report.