The bombings at night are the worst. There is no electricity in the rebel-held portion of eastern Aleppo, and the warplanes flying overhead target any light piercing the blackness beneath.

So families huddle together in the dark, gathered in one room so that they don’t die alone, listening to the roar of the jets and waiting for the bombs to fall.

After they do, rescue workers venture out, navigating the rubble and craters left by earlier bombings, to dig out victims without headlights or lamps. They haul them to hospitals swamped with patients being treated on the floor by doctors who barely sleep and must choose which lives to save and which to let go.

In the small hours of Wednesday morning, it was the turn of two hospitals to be hit in the dark. The hospitals, the two biggest in eastern Aleppo, were struck by bombs shortly after 3:30 a.m., killing two patients and putting the buildings out of use for the victims of more bombings later in the day.

Such is the tenor of life in rebel-held Aleppo, which had become accustomed to regular airstrikes in the four years since rebels seized control of the eastern portion of the city — but nothing like the intensity of the past week.

The collapse of a U.S.- and ­Russian-sponsored cease-fire on Sept. 19 was followed by the launch of a Syrian government offensive, backed by Russian airstrikes, to recapture the neighborhoods held by the rebels. The operation heralded what residents, doctors and medical workers describe as the most ferocious bombardments yet.

At least 1,700 bombs struck eastern Aleppo in the first week after the cease-fire’s collapse, according to the White Helmets civil defense group, a volunteer force funded by the United States and Europe that goes to the aid of people buried by buildings collapsed by bombs. Still, they keep raining down, with new bunker-buster bombs designed to be
used against military installations blasting apartment buildings that house families.

Except that now there is no escape. The challenge of staying alive has been heightened by the complete siege imposed by government troops this month, shortly before the cease-fire was announced.

Hundreds of thousands of people had already fled Aleppo — once a city of 3 million — to refugee camps farther north, to Turkey and on boats to Europe. But the United Nations estimates that 250,000 remain surrounded in eastern Aleppo, many of them the poorest of the poor, the families who couldn’t afford the cost of transportation out of the city.

Now they couldn’t leave if they wanted to. Food is scarce and prices for it are high, and although no one really knows how much Aleppo has stockpiled over many months of fearing just such a siege, it will eventually run out. Doctors have already detected signs of malnutrition in some children, said Caroline Anning of the British charity Save the Children, which estimates that 35 to 40 percent of those trapped in Aleppo are children.

Critically wounded victims who would previously have been evacuated to Turkey must now be treated in makeshift hospitals barely equipped to handle life-threatening injuries. The bombing of the hospitals on Wednesday left just six hospitals functioning, and they are overwhelmed. Only 35 doctors remain, according to the World Health Organization, and 29 according to doctors in the city — down from 30 on Friday after a dentist died in an airstrike, said Adham Sahloul of the Syrian American Medical Society, which runs some of the hospitals.

Only seven of those doctors are surgeons capable of treating the catastrophic wounds inflicted by heavy bombs, the medical charity Doctors Without Borders said in a statement condemning Wednesday’s hospital attacks.

In the past week, the doctors have been handling hundreds of injuries a day. Photographs posted by medical workers show patients lying in pools of blood on hospital floors. Some have been left ­waiting for treatment on the sidewalks outside, according to Mohammed Tariq, a nurse at one of the ­hospitals.

“The doctors are exhausted. Many of them are working until 4 or 5 a.m., and then starting again at 9. They are also scared,” said Maher Saqqur, a surgeon who has been advising the doctors in Aleppo over Skype from his clinic in Canada.

“We have to triage patients, we have to judge whether their cases are hopeless. If they are, it is the hardest thing,” he said. Those with head injuries are being left to die. A man with both his legs blown off was judged too seriously injured to save. Five children died in one hospital on Sunday because there were insufficient resources to treat them.

“We try to make sure they suffer as little as possible, but even the supplies we need to do that are running out,” Saqqur said.

Anesthetics have already been used up entirely at one of the hospitals, said Sahloul, and supplies at others are running low. At the rate at which they are being used now, they could be gone within two weeks, he said, which will add pain to the misery of those being torn apart by bombs.

That hospitals and other vital facilities are being deliberately targeted is not doubted by residents. Only three locations were hit during the strikes carried out early Wednesday — two hospitals and a bakery, where six people were killed as they stood in line to buy increasingly scarce bread.

The White Helmets civil defense teams sometimes intercept the communications of pilots in the planes flying overhead, said Ismail Abdullah, a White Helmets volunteer in Aleppo. “Sometimes we hear the pilot tell his base, we see a market for the terrorists, there is a bakery for the terrorists, is it okay to hit them?” he said. “They say, okay, hit them. Every time they use the adjective ‘terrorists.’ ”

On Sept. 21, two days after the cease-fire collapsed, the White Helmets heard a pilot send a message referring to the “terrorist” civil defense centers, he said. The group passed on the warnings that they might be targeted to U.S. officials in New York, where world dignitaries had gathered for the U.N. General Assembly.

Two days later, in the dark before dawn Friday, the rescuers were struck. They have only four bases in Aleppo and three were targeted. Two were destroyed, along with five vehicles, including a firetruck and an ambulance, said Abdullah.

Those vehicles can’t be replaced. Their loss means rescuers will respond to fewer bombings, save fewer people. Bodies remain buried in the rubble of buildings bombed over the weekend that rescuers couldn’t reach, and now more are piling up, said Ammar al-Selma, the head of the White Helmets teams in Aleppo, who is currently in Turkey.

When teams are too busy to respond to all the bombings taking place, residents are told to write the names of buried families on the debris, so that the bodies can one day be retrieved.

It is grim work. The White Helmets have won international acclaim and prizes for their courage. “Some may think what we are doing is heroic,” their leader, Raed Saleh, told a forum in Washington during a visit to the United States this week.

“But, in fact, it is devastating and depressing beyond belief,” he said. “You are pulling corpses from the rubble. You don’t know if one day that body will belong to your sister, your brother or your friend.”

And the rewards diminish. Selma described how White Helmets rescuers dug one family out of the rubble of a strike last week and transported them to a different neighborhood, only to respond to an airstrike in that neighborhood the following day and find that the family they had saved had been killed.

“This left us without hope. They killed our work. They killed what we did for many hours,” said Selma. “The aircraft sent us a message: We will kill people wherever they go.”

If there were a pattern or timing to the attacks, people would know when to go out to find food and when to take cover indoors, said Abdullah. “They just want to kill everything in sight, so that no one can walk in the streets, so that no one can be saved. They want us all to die,” he said.

As it is, “they can kill you at any time,” said Omar Shaban, a student who described how families cluster in the evenings on the lower floors of his apartment building to escape the bombs. Entire families sleep in one room, because they prefer to die together than to create orphans, widows or bereaved parents.

Shaban, who is 23, married two months ago and spends the evenings sitting in the dark with his new wife, listening to the bombs. They talk about their fears. “I am afraid we will be hungry after two weeks. I am afraid of the airstrikes. I am afraid to lose someone close to me,” he said.

She is afraid of becoming pregnant, he said, and of bringing a child into the world in which they live.

Heba Habib in Stockholm contributed to this report.