A spokesman for UNHCR Adrian Edwards confirmed that the figures precisely referred to people expected to seek refuge by crossing the Mediterranean.
The recent figures and the projections for 2016 denote an increased flow compared to last year, when the agency recorded 219,000 migrant and refugee arrivals in Europe by sea.
The UNHCR had previously estimated 350,000 arrivals in 2015, but on Tuesday, it said 520,000 people had already arrived on Europe's shores this year.
The organization estimated total financial needs at $128 million (114 million euros) from last June through to December 2016.
The organization said that it required an additional $77.4 million to assist countries bearing the impact of the rising flow.
According to the German Foreign Minister, 600,000 refugees have arrived in Germany so far. Frank-Walter Steinmeier said Thursday at the UN General Assembly in New York that Germany can’t cope with the flow of refugees arriving to his country.
Steinmeier called on European nations to show solidarity with Germany.
Greece and Italy which are major entry points for migrants also expressed that there must be more burden-sharing in the EU, especially as they have been hit hard by the Eurozone crisis. Migrants continue to arrive in overcrowded, rickety boats, risking their lives.
David Cameron earlier said that the UK would take 4,000 refugees a year over the next five years, a total of 20,000.
But the number of the refugees arriving in Europe is estimated at 1.4 million. The brutal Syrian civil war has forced at least four million people to leave their homeland and internally displaced more than 7.6 million others.
