UN human rights chief Zeid Ra'ad Al-Hussein described the assault by Syrian regime forces as a “monstrous campaign of annihilation” against the opposition-held territory on the edge of Damascus.
At least 310 people have been killed in the district since Sunday night and more than 1,550 injured, the Syrian Observatory for Human Rights said. At least 38 people died on Wednesday.
UN Secretary-General Antonio Guterres called for an immediate halt to the fighting to allow aid to reach those in need and for the injured to be evacuated.
The bombing meant the 400,000 people trapped in the area “live in hell on Earth,” Guterres told the Security Council.
“We are waiting our turn to die. This is the only thing I can say,” said Bilal Abu Salah, 22, whose wife is five months pregnant in the biggest Eastern Ghouta town Douma.
“Nearly all people living here live in shelters now. There are five or six families in one home. There is no food, no markets,” he told Reuters.
Images from inside the area showed men searching through the rubble of smashed buildings, carrying blood-smeared people to hospital and cowering in debris-strewn streets.
A doctor working in the area told the BBC that the situation is “catastrophic.” “We don't have anything — no food, no medicine, no shelter,” Dr. Bassam said.
“Maybe every minute we have 10 or 20 airstrikes ... I will treat someone — and after a day or two they come again, injured again.”
He said the international community had abandoned the people living there.
Eastern Ghouta, a densely populated agricultural district, is the last major area near the capital still under rebel control. It has been besieged by regime forces for years.
The bombardment of rocket fire, shelling, airstrikes and helicopter-dropped barrel bombs escalated rapidly on Sunday. The assault has devastated the area, indiscriminately ending lives of men, women and children and inflicting horrific injuries. After one airstrike on Wednesday, rescuers pulled four children from the building, but their father was killed, leaving them as orphans, Reuters reported.
Guterres expressed support for a Swedish and Kuwaiti push for the Security Council to demand a 30-day cease-fire in Syria.
Diplomats said the council could vote on a draft resolution in the coming days.
Russia, an ally of President Bashar Assad has called the proposal “not realistic,” but called for a meeting of the council on Thursday to discuss the situation.
A commander in the coalition fighting on behalf of Assad's government told Reuters the bombing aims to prevent the rebels from targeting the eastern neighborhoods of Damascus with mortars.
“The offensive has not started yet. This is preliminary bombing,” the commander said.
Eastern Ghouta is one of a group of “de-escalation zones” under a diplomatic cease-fire initiative agreed by Assad's allies Russia and Iran with Turkey which has backed the rebels.
Mohammad Alloush, the political chief of Jaish Al-Islam, one of the main rebel factions in Eastern Ghouta, said: “There are attempts from some international and local sides for a truce process in Eastern Ghouta and they have not succeeded so far.”