International aid agency Oxfam on Tuesday launched a "12 Days of Giving" appeal to help destitute Syrian refugee families in Jordan and Lebanon survive the region's harsh winter months.

The UN children's agency UNICEF meanwhile warned of the danger posed by another tough winter to millions of children affected by Syria's conflict, including some 1.2 million living as refugees in neighbouring countries.

"Oxfam will be doing the best they can by delivering winter kits to help many of the poorest families," said British actress Michelle Dockery of "Downton Abbey" fame, who last month visited refugees in Jordan who have fled the conflict.

"But they want to be able to do much more and so we really need the public's help."

Oxfam, which aims to raise one million pounds ($1.6 million) for its emergency response, said: "Many people are only wearing the thin summer clothes they fled from Syria in, and those living in tents are sleeping on just a bare mat or thin mattress on the cold winter ground."

Its winter kits for refugees in Jordan and Lebanon include blankets, gas heaters and plastic sheeting. Cash aid and winter vouchers are also to be distributed in Lebanon.

Dockery, star of the worldwide television hit series Downton Abbey, said: "What I have seen and heard on my trip is hard to put into words ...

"Mothers told me their children are already unable to sleep because of the cold and it is only going to get worse" with temperatures falling.

The British government said Tuesday it will match all public donations to the Oxfam appeal.

The United Nations says it has registered more than 2.2 million people who have fled Syria, mostly to Lebanon, Jordan, Turkey, Iraq and Egypt, since the conflict broke out in March 2011. Millions more have been displaced inside the country.

UNICEF said the situation is especially precarious in Lebanon, where thousands of families are living in informal tent settlements on flood-prone land.

"Should tents and latrines be flooded with rain, there is an increased risk of exposure to water borne diseases," it said in a statement.

"Millions of displaced Syrian children have had to find safety under what are, frankly, inadequate living conditions," said Maria Calivis, UNICEF head for the Middle East and North Africa.

"When freezing temperatures and rain are added to the mix, children under five are especially susceptible to opportunistic illnesses like acute respiratory infections which spread easily in overcrowded settings."