The number of Syrians who have fled the war-ravaged country seeking assistance has reached the one million mark, the United Nations refugee agency said.
The UN High Commissioner for Refugees, Antonio Guterres, said the figure is based on reports from his agency's field offices in neighbouring countries that have provided refuge for Syrians escaping the civil war.
With millions more displaced but still inside Syria, Mr Guterres warned the country is "spiralling towards full-scale disaster".
He said the number of refugees has swelled dramatically since the start of the year, with most Syrians pouring into Lebanon, Jordan, Turkey, Iraq and Egypt. Their presence is severely straining the resources of host countries and the international donor community.
Mr Guterres said: "With a million people in flight, millions more displaced internally, and thousands of people continuing to cross the border every day, Syria is spiralling towards full-scale disaster."
Syria's uprising began in March 2011 with protests against president Bashar Assad's authoritarian rule.
When the government cracked down on demonstrators, the opposition took up arms and the conflict turned into a full-blown civil war. The United Nations estimates more than 70,000 people have been killed. The relentless violence has devastated many cities and forced hundreds of thousands of Syrians to seek refuge abroad.
More than 400,000 people have become refugees since January 1, and often arrive in neighbouring countries "traumatised, without possessions and having lost members of their families", Mr Guterres said. Around half are children, with the majority under the age of 11.
"We are doing everything we can to help, but the international humanitarian response capacity is dangerously stretched," he said. "This tragedy has to be stopped."
The UN in December estimated that 1.1 million Syrian refugees would arrive in neighbouring countries by the end of June. At that time its regional response plan was only 25% funded, and it is now in the process of adjusting it in light of the new figures, Mr Guterres said.