The United Nations says the civil war in Syria has forced more than three million people to flee the country, an increase of one million in the past year alone.
Antonio Guterres, the UN High Commissioner for Refugees (UNHCR), called the crisis "the biggest humanitarian emergency of our era" on Friday, with almost half of all Syrians forced to abandon their homes since the conflict began in March 2011.
"The Syrian crisis has become the biggest humanitarian emergency of our era, yet the world is failing to meet the needs of refugees and the countries hosting them," he said.
"The response to the Syrian crisis has been generous, but the bitter truth is that it falls far short of what's needed."
The agency said its work to help the Syrian refugees now marked the largest operation in its 64-year-history.
Al Jazeera's Rula Amin, reporting from a refugee camp in the Bekaa Valley in Lebanon, said many of the refugees thought the fighting would resolve in a few months, but are now resigned to the conflict raging on.
A total of 6.5 million Syrians have been displaced from their homes, representing about 30 percent of Syria's pre-war population of 23 million.
Over half of all those who uprooted are children, the UN said, describing "cities where populations are surrounded, people are going hungry and civilians are being targeted or indiscriminately killed".
Most of the Syrian refugees have found their way to neighbouring countries, with Lebanon hosting 1.14 million, Jordan 608,000 and Turkey 815,000.
The influx is placing an overwhelming burden on the host countries, the UNHCR stressed, adding that nearly 40 percent of the refugees were living in sub-standard conditions.
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The UNHCR said families were arriving in neighbouring countries "in a shocking state, exhausted, scared and with their saving depleted."
The agency also voiced deep concern for several hundred Syrians trapped inside the remote al Obaidi refugee camp in Iraq after UN agencies and other groups were forced to abandon their offices and warehouses as the region became overrun by the Islamic State group.
In a statement, David Miliband, former British foreign secretary and the current head of the International Rescue Committee, said: "The three million refugees from the Syria conflict represent three million indictments of government brutality, opposition violence and international failure."
The increasingly fragmented conflict raging in Syria has claimed more than 191,000 lives since erupting in March 2011.