Hassan Khalaf, director of Shifa hospital, said the intensive care unit could be rendered useless and lives were being put at risk.
"These patients are directly threatened," he said. "The first threat they face because of the power cut is their low temperature and the lack of oxygen."
One dialysis patient told Al Jazeera: "I am a kidney failure patient. When a power cut takes place, all dialysis machines stop. We will then suffer from blood clots."
Israel closed all of its crossings with Gaza on November 5, citing rocket attacks from Palestinian fighters inside Gaza.
Al Jazeera's Sherine Tadros reporting from Gaza, said: "We heard from Israeli officials that around 40 trucks would be allowed into the Gaza Strip, about 10 of those would go straight to the UN camps ... all the trucks will contain humanitarian aid, but no fuel as of yet has reached Gaza.
"The trucks will only be enough to last for about one more week and criticism of aid agencies here is that Israel continues to trickle in the goods and never brings in enough. It's literally a day-by-day existence."
|Frequent power cuts stall the treatment needed for kidney patients [AFP]
Although electricity is still being supplied to Gaza by Israel and Egypt, it is not enough to prevent regular power cuts.
On Saturday, doctors at Shifa hospital had to abandon using electronic equipment in the newborn baby unit when there was a power failure, Mohyeldin reported.
"When there was a power cut, the generator kicked in, but it had a problem," he said.
"As a result, all the machines shut down and staff had to manually pump oxygen to all the infants here."
Stocks of about 160 essential medicines have run out, while about 120 other healthcare drugs are running low, the hospital has said.
"It is indispensable to have all the supplies because we cannot continue working manually for a long period. Yesterday we had to transport oxygen cylinders to the beds," Radwan Hasoun, a manager of Shifa's intensive care unit, said.
"We want the frontiers opened and the siege to be lifted, so we can participate in the progress of the world like other people."
UN aid shortages
The delivery of United Nations aid to nearly two-thirds of Gaza's 1.5 million people has also been severely affected by the blockade.
The UN has said that it only has enough supplies in Gaza to last a few more days, unless the Israeli restrictions on the territory are lifted.
Amid the closures, Israeli army forces have launched several raids into Gaza, killing more than a dozen Palestinians.
Several Israelis have been injured by rockets fired by Palestinian fighters into Israel in recent days.
Israel and Palestinian Hamas, which has de facto control of the Gaza Strip, have observed a shaky ceasefire deal since July but the agreement is due to expire next month.
Israel is holding a US-backed peace dialogue with the Palestinian Authority, which is led by Mahmoud Abbas, Palestinian president and leader of the rival Fatah faction.
Hamas, deemed a "terrorist" organisation by Israel, is not a party to the negotiations.