The United Nations refugee agency says over 31,000 South Sudanese, fleeing famine and conflict, have crossed the border into Sudan so far this year.
A statement from the office of the United Nations High Commissioner for Refugees (UNHCR) in Khartoum said on Monday that more than 80 percent of the latest arrivals were women and children.
"Initial expectations were that 60,000 refugees may arrive through 2017, but in the first two months alone, over 31,000 refugees arrived," the statement read.
Sources say many of the refugees are exhausted, malnourished and ill after having walked for days.
Sudan is hosting about 328,339 refugees, who fled civil war in South Sudan that erupted in late 2013.
Fighting between government forces of President Salva Kiir and rebels led by the former vice president, Riek Machar, has caused a mass exodus in the troubled region. The fighting has uprooted more than three million people over the past years.
The Central African Republic, the Democratic Republic of the Congo, Ethiopia, Kenya, and Uganda are also hosting thousands of refugees from South Sudan.
The UN says the continuing migration presented "heightened risks of prolonged (food) underproduction into 2018" across South Sudan.
The UN declared famine last week in parts of South Sudan's Unity State. The international body says about 5.5 million people are expected to have no reliable source of food by July.
The UN Children's Fund (UNICEF) has also recently warned that at least 270,000 children in South Sudan are suffering from malnutrition.
The country gained independence in July 2011, but descended into war in December 2013, after President Kiir accused Machar of plotting a coup to usurp power.
Numerous international attempts to reach a truce between the warring sides have failed.