Medical evacuations in the rebel-held eastern Ghouta region got underway on Wednesday after months of delays, announced the International Committee of the Red Cross.
"Tonight the @SYRedCrescent with @ICRC team started the evacuation of critical medical cases from #EasternGhouta to #Damascus," the ICRC said on its verified Twitter account.
Pictures posted with the tweets appeared to show a convoy of ambulances ready to move the critically ill patients from the Damascus suburb.
The Syrian American Medical Society, another medical relief organization, said the evacuations covered "29 critical cases, approved for medical evacuation to Damascus. Four patients were evacuated today."
It said the remainder would be evacuated in the coming days.
Eastern Ghouta is one of the last remaining rebel strongholds in Syria and has been under a tight regime siege since 2013, causing severe food and medical shortages for some 400,000 residents.
The Syrian Red Crescent said in a tweet that its volunteers "just started to transfer cases in need of medical care from east Ghouta to hospitals in Damascus after long negotiations".
Last week, Jan Egeland, the head of the UN's humanitarian taskforce for Syria, warned that at least 16 people had died while waiting for evacuation from Eastern Ghouta.
He said a list put together several months ago of nearly 500 civilians in desperate need of evacuation was rapidly shrinking.
"That number is going down, not because we are evacuating people, but because they are dying," he told reporters in Geneva.
"We have confirmation of 16 having died on these lists since they were resubmitted in November, and it is probably higher," he said, highlighting the case of a baby who died on December 14, as the latest round of Syria peace talks in Geneva ended in failure.
Egeland said evacuations and efforts to bring aid into the region had been blocked by a lack of authorizations from the Syrian authorities.