Three million migrants are expected to arrive in Europe by 2017 as they flee war in Syria and other conflict zones, with a small positive impact on the EU economy likely, the EU’s executive arm said on Thursday.

Three million migrants are expected to arrive in Europe by 2017 as they flee war in Syria and other conflict zones, with a small positive impact on the EU economy likely, the EU's executive arm said on Thursday.

"Overall, an additional three million persons is assumed to arrive in the EU over the forecast period," the European Commission's economic forecast for 2015-2017 said, in its first assessment of the effect of the migrant crisis.

It predicted that there would be one million arrivals in total during 2015, soaring to 1.5 million in 2016 and then decreasing to half a million in 2017.

That would represent an 0.4 percent EU population increase once unsuccessful asylum applications were taken into account, it said.

European Union economic commissioner Pierre Moscovici said that the migrants could help boost the EU economy.

"There will be an impact on growth that is weak but positive for the EU as a whole, and that will increase GDP (Gross Domestic Product) by 0.2 to 0.3 percent by 2017," Moscovici said.

"That will combat a certain number of received ideas and backs the politics of President (Jean-Claude) Juncker," who has pushed for the EU to do more to help migrants, Moscovici added.

The migrant arrivals would create a short term boost to growth from higher government spending on new asylum seekers, the Commission said.

That would be followed by a medium-term boost because of an increase in the number of workers available "provided the right policies are in place to facilitate access to the labour market," it said.