Conditions near the Syrian capital of Damascus are so desperate that women are giving birth underground and people who venture out in the day-time risk injury or death from the relentless bombing, Christian Aid is warning.
The charity said the onslaught against people, schools and hospitals in the besieged Eastern Ghouta area of rural Damascus is so overwhelming that those still alive have retreated to cellars and basements without water or electricity.
Christian Aid's Máiréad Collins said: 'Conditions for people trapped in Eastern Ghouta amount to a living hell.
'People, many displaced from elsewhere in Syria, are forced to find shelter in basements without proper access to electricity or water. Local NGOs' attempts to deliver humanitarian support are dangerous and severely limited.
'An immediate ceasefire is absolutely imperative, for the 400,000 children, old people, women and men still caught in Eastern Ghouta.'
Christian Aid's local partner organisation runs a food kitchen in Eastern Ghouta. 'As things stand, they will have to run the kitchen at night and distribute meals before 6am, when the shelling begins,' the charity said.
Indiscriminate shelling of East Ghouta has intensified dramatically, according to the United Nations, which warned that 'the international crimes of indiscriminate bombardment and deliberate starvation of the civilian population' are taking place in Syria.
'Reports of at least 200 people killed in just 72 hours last week in Eastern Ghouta stand as a reminder that Syria is not yet somewhere to which refugees can safely return,' Christian Aid said.
The charity is supporting the UN's call for an immediate ceasefire and for medical evacuations and humanitarian work to be allowed to proceed.