Around 500 civilians have died in a relentless bombing campaign in eastern Ghouta in recent days
International pressure is being put on Syria to observe a 30-day humanitarian ceasefire.
It comes amid reports that Syrian-Government forces have begun a ground offensive to try to enter the rebel-held of eastern Ghouta near Damascus.
The area has suffered a relentless bombing campaign resulting in around 500 civilian deaths in recent days.
A resolution demanding a ceasefire was passed by the UN Security Council last night – However it is unclear exactly when the truce will start.
It is hoped the cease-fire will allow aid and medical evacuations into the besieged area.
Russian-backed Syrian forces continued to pound the rebel-held suburb of Damascus – with the week's reported death toll standing at more than 500 civilians - including 127 children - by Saturday night.
It is not clear exactly when the truce will start but Sweden's UN ambassador Olof Skoog said before the vote that the "UN convoys and evacuation teams are ready to go."
Speaking after the vote, US ambassador to the UN Nikki Haley said: "We are late to respond to this crisis, very late."
The resolution's sponsors, Kuwait and Sweden, had adjusted the resolution late on Friday in an effort to gain the support of Russia – an ally of Syrian President Bashar al-Assad and holder of a Security Council veto.
Moscow, which intervened militarily in support of President Bashar al Assad in 2015, has denied any direct involvement in the eastern Ghouta bombardment.
The resolution changes included dropping a demand that the ceasefire take effect in 72 hours, a deadline Russia's UN ambassador Vassily Nebenzia had described as unrealistic.
Instead, the language was changed to "without delay" and the word "immediate" was axed in relation to aid deliveries and evacuations.
The remaining text says that 5.6 million people in 1,244 communities are in "acute need," demanding that all sides "cease depriving civilians of food and medicine indispensable to their survival."
However, the ceasefire does not apply to fighting against Islamic State, al Qaeda or "individuals, groups, undertakings and entities" associated with them.
This means the Syrian regime of President Assad can continue fighting jihadists in Idlib who are linked to al Qaeda. Idlib is the last Syrian province not in government hands.
Meanwhile, in eastern Ghouta, many residents were hiding in underground shelters with little food or medical supplies as Assad's government forces continued their bombardment.
On Thursday, UN secretary general Antonio Guterres said the Syrian government's bombing campaign had turned the region into "hell on Earth" for civilians.
Syria's war has now been running for seven years.