IN THE largest exodus of refugees for months, as many as 20,000 Syrians have fled their war-torn country in just 24 hours, as the humanitarian crisis caused by the 20-month-long conflict worsened.

The United Nations refugee agency reported the surge of refugees, which means that there are now more than 408,000 Syrian refugees living in neighbouring countries.

Syrian government troops and rebel fighters are engaged in fierce fighting near the Turkish border, prompting more civilians to flee into Turkey, activists say. Heavy shelling and air raids have been reported in Maaret al-Numan and other rebel-held areas.

''Some 20,000 have fled areas near the Syrian-Turkish border in the past 24 hours,'' said Rami Abdel Rahman, the head of the opposition Syrian Observatory for Human Rights.

With the bitterly cold winter months approaching, concern is mounting for the health and safety of the refugees fleeing Syria, with many surviving in abandoned schools, shopfronts, crowded into private homes or in burgeoning UN-run camps.