Palestinians wait in line to buy bread outside a bakery in Gaza City on Wednesday. (Khalil Hamra/Associated Press)

Food and medical supplies are trickling into Gaza, aid agencies said Wednesday, warning a lull in violence is urgently needed to stem a deteriorating humanitarian situation.

John Holmes, the United Nations under-secretary general for humanitarian affairs, said roughly 115 trucks filled with supplies crossed into Gaza Tuesday and Wednesday.

Gaza's main power plant shut down on Tuesday because no fuel has entered the Palestinian territory in the past three days. Roughly 650,000 Palestinians in central and northern Gaza will be without electricity for 16 hours for each day, he said.

Some medical supplies are getting in, but the flow is "difficult and fragile," he said. About five ambulances crossed into Gaza on Tuesday, along with generators for hospitals.

Gaza has been closed since Saturday, when Israel launched an air campaign against Hamas, the militant organization that governs the territory. Hamas increased its rocket attacks against Israel last week following the expiration of a shaky six-month ceasefire.

Aid workers disappointed

An ultra-Orthodox Jewish man looks at the damage to the classroom of a school caused by a rocket fired by Palestinian militants in Gaza, in the southern Israeli city of Beersheba on Wednesday. (Tara Todras-Whitehill/Associated Press)

Palestinian officials say roughly 390 Palestinians have been killed in the past five days. The UN estimates about 60 of those killed were civilians. Four Israelis have died in the rocket attacks, according to officials.

Both sides have rejected a French proposal for a 48-hour ceasefire to deliver supplies to Gaza's 1.4 million residents.

Karen AbuZayd, the commissioner general for the UN Relief and Works Agency (UNRWA), said aid workers were optimistic the short lull would help the roughly 750,000 Palestinians who receive food aid.

"They were very disappointed because they were quite cheerful thinking ‘Oh good, this is going to stop for a couple of days and we’ll be able to get things in and have a little bit of peace from the bombs and the noise of the drones overhead,' " said AbuZayd.

"So [it was] a great disappointment once the expectations were raised and then ... dashed."

Lineups for bread

Al-Jazeera reporter Ayman Mohyeldin, who is in Gaza City, said food and humanitarian supplies are scarce, even though Israel has allowed about 4,300 tonnes of essentials into the region during the past three days.

"Every day we wake up and see long lines at bakeries, at the supermarkets, at the food stores," he said. "Whatever people can get, they're trying to get."

UNRWA, which suspended food delivery to roughly 750,000 Palestinians on Dec. 19, will resume food distribution Thursday for a few days.

"We have been able to get lots of trucks in over the last two or three days," said UNRWA spokesperson Christopher Gunness. "We have enough just for days."

Israeli trucks drive the supplies to an open field where they are offloaded and repacked onto Palestinian trucks, which drive across the Gaza border. The delivery chain must shut down at night, said UNRWA officials.

Hospitals rely on generators

Agencies such as the International Red Cross and Palestinian Red Crescent say hospitals are running low on medicines, blood and surgical kits.

Without power, hospitals must rely on backup generators throughout the day, exhausting their two-week supply of fuel, said UN officials.

Gunness said emergency wards are collapsing under the volume of patients.

"If you have a foot blown off and it's not life-threatening, then you probably won't be seen. If what you have is life-threatening, then with luck, you will be," he said.

A number of countries have responded to UNRAW's emergency appeal for Gaza and the West Bank, including Britain, the U.S., China, Norway and Lebanon.

With files from the Associated Press, Reuters