* Refugee numbers nearly doubled this year - UNHCR
* U.N. says refugee plan only 25 percent funded
* No end in sight for Syria's civil war
One million people have fled Syria's civil war, piling pressure on the country's neighbours who are struggling to support them, the United Nations refugee agency said on Wednesday.
Around half the refugees are children, most of them aged under 11, and the numbers leaving are mounting every week, UNHCR added.
"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," UN High Commissioner for Refugees António Guterres said in a statement.
"We are doing everything we can to help, but the international humanitarian response capacity is dangerously stretched. This tragedy has to be stopped."
Nearly two years ago, Syrians started trickling out of the country when President Bashar al-Assad's forces started shooting at pro-democracy protests.
The uprising has since turned into an increasingly sectarian struggle between armed rebels and government soldiers and militias. An estimated 70,000 people have been killed.
UNHCR said the number of Syrians quitting their country has increased dramatically since the beginning of the year with more than 400,000 - nearly half the total figure - since Jan. 1st.
They arrive traumatised, without possessions and having lost members of their families, it added.
Most have fled to Lebanon, Jordan, Turkey, Iraq and Egypt and some arrive in North Africa and Europe.
Lebanon - the country closest to Syria's embattled capital of Damascus - is the smallest of the country's neighbours but has received the most refugees.
Including Syrian workers and self-supporting Syrian families, one in five people in Lebanon is now Syrian.
Refugee flows into Lebanon have doubled to 4,400 a day in the past three weeks, UNHCR representative in Lebanon Ninette Kelley told Reuters in an interview.
But despite pledges of $1.5 billion by international donors for a U.N. response plan to help Syria's displaced, only 25 per cent has been funded, UNHCR said.
In Jordan, energy, water, health and education services are being strained to the limit, the agency added. Turkey has spent more than $600 million setting up 17 refugee camps, with more under construction.
There is no end in sight for Syria's civil war and international powers are divided over how to respond to it. Russia and Shi'ite Iran support their historical ally Assad while the United States and Sunni Muslim Gulf countries back the opposition.
Both Damascus and the opposition have said they will consider peace talks but no meetings have been arranged.