More than 60,000 South Sudanese have entered Sudan since January, United Nations High Commissioner for Refugees (UNHCR) said on Wednesday.
The UN refugee agency said the South Sudanese have been fleeing from famine and war in the world's youngest nation.
Formed after splitting from the north in 2011, South Sudan, has declared a famine in parts of the country where 100,000 people are said to be facing starvation.
The UN refugee agency, which was initially expecting 60,000 South Sudanese refugees to arrive in Sudan in the whole of 2017, said the figure has already surpassed their expectations in the first three months.
"The number of new arrivals has surpassed expectations, signalling a likely worsening situation in South Sudan," UNHCR said in a statement on Wednesday.
UNHCR anticipates a continuous influx of South Sudanese refugees throughout this year, but is concerned about a drop in funding to meet their needs.
Aid groups have denounced a "man-made" famine caused by bloodshed in South Sudan where civil war has forced people to flee, disrupted agriculture, sent food prices soaring and cut off aid agencies from some of the worst-hit areas.
South Sudan has been engulfed by war since 2013 after President Salva Kiir accused his rival and former deputy Riek Machar of plotting a coup.
More than 365,000 South Sudanese refugees, most of them women and children, have arrived in Sudan since December 2013.