Thousands of Syrian refugees living in makeshift camps in Lebanon were weathering a winter storm on Wednesday that brought snow, rain and freezing temperatures to the country.

In northern Arsal, just across the border from Syria, layers of snow sat atop flimsy shelters housing tens of thousands of recently arrived refugees.

The UN refugee agency UNHCR has worked around the clock, partnering in recent days with the Lebanese army, to distribute winter supplies including thermal blankets and money for heaters.

But despite the efforts, UNHCR spokeswomen Lisa Abou Khaled said there were concerns for thousands of people living in more than 200 informal camps in central and north Lebanon.

"We are worried, because it is really cold in the Bekaa region, and we're extremely worried about the refugees living in makeshift shelters, because many are really substandard," she said.

Abou Khaled said UNHCR had prepared stockpiles of items including plastic sheeting, floor mats, blankets and mattresses to help refugees whose shelters might be flooded or destroyed by the storm.

She said winter supplies had also been handed out to local municipalities, so they could quickly respond to emergency needs.

In Arsal, temperatures hovered just above zero degrees centigrade, and the forecast predicted between three and five inches (7.6 and 13 centimetres) of snow and night time temperatures of minus four degrees.

In the past few months, more than 20,000 new refugees have arrived in the Arsal region, overwhelming the small town.

"The Syrian refugees here are shivering with cold, especially the ones in tents," said Wafiq Khalaf, a member of Arsal's municipal council.

"Water has come into the tents from the roofs, and from the ground where there is flooding," he told AFP by phone.

"At the moment there is more than 10 centimetres of snow on the ground, but more is expected," he added.

Despite the conditions, Khalaf said refugees were continuing to arrive, including a group of 10 families fleeing the Syrian town of Yabrud in the Qalamoun region north of Damascus.

More than 835,000 Syrian refugees are registered in Lebanon, although the real number is thought to total more than one million.

Thousands live in makeshift camps, in shelters made of little more than plastic sheeting nailed to wooden frames.

Others are living in unfinished buildings with only slightly more protection from the elements in cities including the capital Beirut.