KILIS, Turkey — Hundreds of thousands of Syrian civilians have fled rebel-held parts of the city of Aleppo in recent weeks under heavy aerial bombardment by the Syrian government, emptying whole neighborhoods and creating what aid workers say is one of the largest refugee flows of the entire civil war.

The displaced, as many as 500,000 to date, the United Nations says, have flooded the countryside, swelling populations in war-battered communities that are already short on space and food and pushing a new wave of refugees into Turkey, where in interviews many have described a harrowing journey that left them in desperate condition, broke, hungry and, in many cases, sick or wounded.

Much of the human tide flowing out of northern Syria has crashed on this once-quiet border town, where Syrians now nearly outnumber the original 90,000 Turkish inhabitants.

Its sidewalks are covered with destitute Syrians hawking cookies, coffee and cigarettes, and rents have skyrocketed as Syrian families have crowded into apartments. Ambulances regularly scream through town, ferrying war victims to the city’s overburdened medical facilities.