A wave of 21,000 Syrian refugees in the past week, moving into northern Jordan at about five times the usual daily rate, has overwhelmed this crowded camp that's already struggling with flooding, short supplies and tent fires.

As newly arrived refugees unpacked on Monday, one family's tent went up in flames after kerosene spewed onto a nearby heater. Black smoke poured into the sky. The family's meager possessions were incinerated. In a sign of frustration, some refugees pelted a fire truck with stones, cracking its windshield, saying the firefighters were slow to respond.

"Almost every day, one or two tents catch fire," said 22-year-old Abu Anis, who like most refugees interviewed at the camp asked to be identified by his nickname because they feared retaliation against relatives still living in Syria. "Thank God, other people haven't been hurt because the tents are so close together."

The United Nations says the huge influx of Syrian refugees crossing into neighboring Jordan during the past week was larger than anticipated and left its agencies, already suffering from a funding shortfall, reeling under the influx. U.N. officials are crying out for more funding as they rush to build showers, toilets and a school for the newcomers.

The UNICEF representative to Jordan, Dominque Hyde, said more than 21,000 Syrian refugees arrived at Jordan's sole refugee camp just in the past week.

"We were expecting larger numbers in the new year, but not the 3,000 a day that have been coming across to Zaatari camp," she said.

New arrivals — most of them coming from southern Syria where fighting has been intense — were crossing into Jordan at about five times the rate anticipated, according to Andrew Harper of the U.N. refugee agency in Jordan. Until recently, an average of 700 refugees arrived at the desert facility each day.

International donors have pledged less than 3 percent to a $1 billion U.N. appeal made last month to aid the more than 670,000 Syrian refugees estimated to have fled to surrounding countries during the 22-month uprising to topple President Bashar Assad. The U.N. says it hopes a donor conference for Syrian refugees Wednesday in Kuwait will rectify the dire funding situation.

Harper said the Jordanian government has done what it can to provide protection to the 320,000 Syrian refugees it now hosts, but it cannot continue to bear the strain. The U.N. refugee agency said Syrian refugees in Jordan required about $500,000 in assistance. About one-fifth the refugees live in the camp, while the rest shelter in mainly northern communities.

Crossing into Jordan was frightening for Abu Nidal, a 50-year-old farmer from near the Golan Heights. He and 180 others, including women and children, were forced to row across territory flooded by waters from the Yarmouk River.

"The women and children were so afraid because the small boats were rickety and the water (was) deep," he said. "It took eight hours, but we finally arrived safely with the help of the young men and the Jordanian army."

Hyde said the influx to the camp means more showers, toilets, shelters, and schools need to be built. And more refugees also means a rising demand for water in Jordan, already the fourth most water scarce country in the world. She described the sharp increase in refugees as "daunting."

"You can see that many children at Zaatari — called the 'kids' camp' because they make up the greatest numbers here — don't have socks or even shoes in the dead of winter," she said as children played on swings and slides nearby.

Hyde said 24,000 Syrian refugee children entered Jordan in the past month alone — the highest number ever.

"This means that we need to be building a new school immediately," she said, expressing hope that a new one could be constructed by mid-February.

Classes are to resume at the existing school on Feb. 5, but desperate refugees moved in earlier this month because howling winter winds blew their tents down and others were flooded. They say they are still awaiting alternative accommodations. Other camp residents have started jokingly describing the school as "occupied territory."

"We've had officials come and visit — even the Bahraini government who built the school — and still no one has responded to our needs for new housing," said Abu Mohamed, a 35-year-old businessman who is staying in the school where about two dozen people share a single classroom partitioned by rows of desks.

"They haven't given us heaters, tents or trailers," said the man who fled fighting in the Syrian capital, Damascus, with his family of four. "Rain is forecast again. Doctors tell us at the camp hospital that our children are sick from the cold."

Anne Richard, the U.S. assistant secretary of state for population, refugees and migration, says that as more Syrians pour out of their homeland, more countries are needed to contribute assistance.

Last year, the U.S. contributed $220 million to assist Syrian refugees. Speaking Monday in the Jordanian capital, Richard said the U.S. would announce additional funding for Syria at the conference in Kuwait, but declined to provide details.

Another Abu Walid, 46, from the southern Syrian town of Dara'a, said that as much as he and the other refugees need the aid, what they really want is an end to nightmarish killing, rape and shelling back home. His 16-year-old son was killed in Syria by shrapnel from artillery tank fire as he walked home from work.

"We want this awful crisis to end and to return home," said the slender man, a wool scarf tied around his neck to ward off the cold.

"The world is sleeping. It's failing us. ... How can it continue to turn its back on us every day as more and more are killed inside Syria?"