Aid agencies, including the Red Cross and World Food Programme, are calling for an urgent ceasefire to allow them to reach the besieged Syrian enclave of eastern Ghouta, as rockets and barrel bombs dropped by pro-regime forces killed dozens more people on the fourth day of an intense assault.

The calls were echoed by the UN secretary-general, António Guterres, who demanded an immediate suspension of “all war activities” in the rebel-held Damascus suburb, which he described as a “hell on earth”.

The UN’s high commissioner for human rights, Zeid Ra’ad Al Hussein, also called for an immediate halt to hostilities, warning that “civilians were being slaughtered in droves”.

The UN Security Council is expected to vote, probably on Thursday, on a draft resolution demanding a 30-day ceasefire to allow deliveries of aid and medical evacuations.

Terrified residents in the area, where 400,000 people are trapped on the outskirts of Damascus, were sheltering in caves, dugouts and basements, as a hail of explosives hit homes, roads and hospitals amid what aid officials warned was an unfolding “humanitarian catastrophe”.

The attacks have killed over 335 civilians since Sunday, the UK-based Syrian Observatory for Human Rights said on Thursday. More than 1,200 others have been injured, a toll people on the ground say has been exacerbated by attacks on hospitals, clinics and ambulances.

In its statement, the International Committee of the Red Cross said medical personnel in eastern Ghouta were unable to cope with the high number of wounded, adding that “wounded victims are dying only because they cannot be treated in time”.

The call for a pause in the fighting to allow food and medical aid to reach eastern Ghouta came as some international agencies, who work with local partners in the densely populated agricultural area on the outskirts of Damascus, announced they were suspending their programmes because of the risk.

The halting of aid efforts in an area that has seen one small convoy of aid enter since November comes as acute malnutrition levels among children in the enclave have quadrupled in less than a year to the highest levels seen in Syria’s seven-year war.

“Just a cup of water or a piece of bread may cost a man his life because he is under attack from missiles,” said Dr Fayez Orabi, one of the doctors in eastern Ghouta. “They cannot get out of their shelters.”

There has been widespread condemnation from the United Nations and politicians around the world, but without any action to halt or lessen the bombardment. “It is a miserable situation, the whole world just watching us,” said Orabi.

Photographs and videos sent from inside the enclave showed bloody, fractured bodies and the aftermath of the strikes. In one a weeping father seizes his son’s tiny body from the bed of a truck taking it to burial, for one last embrace.

The surge in killing in Ghouta came amid reports of an impending regime incursion into the area, as forces loyal to President Bashar al-Assad look to regain control of a a rebel stronghold that was once the capital’s breadbasket.

“The offensive has not started yet. This is preliminary bombing,” a commander in the coalition fighting on behalf of Assad’s government told Reuters.

Aid officials interviewed by the Guardian in Damascus and elsewhere described the situation in eastern Ghouta as a “hell on earth” in particular for the estimated 200,000 children trapped in an area, with some 67 children reportedly among the fatalities recorded in the last few days.

Even before the current intensification of the government’s bombardment, experts were warning that food prices in the besieged area had made it impossible for many residents to afford a meal with a basic portion of bread costing a staggering 85 times as much as in Damascus 10 miles away, and with a cylinder of cooking gas – available for $44 (£31) in the capital – selling for up to $300 in eastern Ghouta.

Among agencies announcing that the violence had made continued work impossible was Care, whose Syria country director, Wouter Schaap, warned of a “humanitarian catastrophe” if a ceasefire was not agreed.

“The situation in eastern Ghouta is more critical than ever. Despite their resilience for years, people are giving up hope for survival.

“Unlike previous airstrikes, destruction has reached every area this time. There is no place for people to go – no shelter, no safety,” said ‘Hanaa’, who works in eastern Ghouta with a local organisation supported by Care.

The UNRWA, the UN agency that supports Palestinian refugees in Syria, said it was also suspending food aid and schooling after two of its students were killed in a mortar attack in a move it said would affect 27,000 children.

Juliette Touma of Unicef also painted a bleak picture. “What we know that is that needs are dire in eastern Ghouta. It is impossible to compare suffering with suffering [in Syria] but it is truly horrific. It is a hell hole. A killing field for children.”

Jakob Kern, the World Food Programmes’s chief in Damascus, added: “Since it intensified it is no longer a question for civilians of basic needs. It is about survival. It’s a question of, do I live through this day.

“Two two weeks ago we managed to deliver enough food for 7,000 people in the first convoy in three months. Less than 2% of the people who needed it got aid. We have asked and asked just about everyone for a pause but realistically we need a month’s halt in the fighting to deliver a month of rations.”