The UN says there has been a huge leap in the numbers of Syrian refugees arriving in Jordan, putting a considerable strain on resources.
A UN official told the BBC that up to 3,000 were arriving every day and at least 50,000 were waiting to cross.
Jordan has already warned that if there is a mass influx of refugees it will close the border with Syria.
The BBC's Fergal Keane at the Zaatari refugee camp in Jordan says many there feel abandoned by the outside world.
The UN refugee council (UNHCR) said on Wednesday that more than 26,500 Syrian refugees had crossed into Jordan since 1 January, with more than 10,500 new arrivals in the past five days alone.
That compared with 16,413 arriving in December; 13,000 in November and 10,000 in October.
The conflict in Syria began almost two years ago with demonstrations against the government of President Bashar al-Assad.
The protests quickly turned violent as opponents of Mr Assad took up arms to try to resist a brutal crackdown by the authorities.
The conflict has left more than 60,000 people dead and two million internally displaced.
The UNHCR says there are now more than 670,000 registered Syrian refugees and people awaiting registration in Jordan, Turkey, Lebanon, Iraq and Egypt.
International efforts to resolve the crisis have stalled, with the government refusing to discuss Mr Assad's departure and the opposition rejecting anything short of his removal.
'No support from anyone'
Andrew Harper, the UN's humanitarian co-ordinator in Jordan, has appealed for increased international aid.
"It's extremely critical," he told the BBC.
"We know that we've done as well as we can given the resources we've got… we've got no resources any more. We need money now desperately to expand this camp as well as open two others."
The UN in Damascus recently confirmed that it had received pledges of only 3% of what it had asked for in its 2013 Syria appeal.
Our correspondent says new arrivals at the main Zaatari refugee camp in Jordan are issued with four blankets each and every family is given a tent.
But many are angry at the lack of international help.
"What good are your cameras? We are getting no support from anyone," one man told the BBC.
Another said he felt the international community was simply looking on at Syria's tragedy "as if they were looking through a window. Where is the humanity?"
Troops from the Jordanian border patrol monitor the influx of Syrians fleeing the 22-month-old uprising.
A woman called Fatima told the BBC at the Zaatari camp that she, her husband and three children had decided to flee after their house was destroyed by shelling in Deraa.
"There is no food, no work… the children are crying all the time," she said.
Most refugees come by foot, guided to the crossing points by Free Syrian Army rebels and then met by Jordanian soldiers on the other side.
The camp, near the town of Ramtha inside the Jordanian border, is a vast sprawl of tents and some pre-fabricated buildings in the desert.
There is medical care at the camp and agencies such as Unicef and Save the Children provide trauma counselling. There is also some schooling, but our correspondent says the increasing number of people arriving means an ever-growing strain on existing resources.
Separately, the UN Food and Agricultural Organisation on Wednesday warned there had been a massive drop in Syria's agricultural production.
The conflict was destroying infrastructure and irrigation systems, and making it harder to harvest crops, it said. Wheat and barley production had fallen from about four million tonnes in normal years to two million tonnes in 2012.
About 46% of the Syrian population depend on agriculture for their livelihoods, the UN says.