Three million refugees and migrants could arrive in the European Union by 2017, according predictions made by the EU's executive arm.

The European Commission has estimated one million arrivals in total during 2015, soaring to 1.5million in 2016 and then decreasing to half-a-million in 2017.

However, once unsuccessful asylum applications have been taken into account, this will only represent a 0.4 per cent population increase.

In addition, European Union economic commissioner Pierre Moscovici said that the influx of refugees and migrants from 2015-2017 will end up boosting the EU's economy.

Saved: More than 500 men, women and children were rescued by the Spanish navy after the boat their were travelling on to attempt to make it across the Mediterranean sailed adrift off the Libyan coast on Thursda

'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.

This comes as the Spanish navy were called out to rescue more than 500 men, women and children whose small wooden boat had sailed adrift off the coast of Libya on Thursday morning.

Rescued: The 517-strong group, which included two babies, had packed onto a 66ft-long fishing boat in an attempt to cross the Mediterranean from Libya

The rescue operation lasted more than six hours, the ministry said, as Spanish navy personnel ferried refugees to their ship on board small inflatable, motorised boats

The 517-strong group, which included two babies, had packed onto a 66ft-long fishing boat in an attempt to cross the Mediterranean.

The rescue operation lasted more than six hours, the Spanish Ministry of Defence said, adding that the group is now heading towards the Italian port of Lampedusa where the migrants and refugees will embark and be processed.

EU autumn economic forecasts released on Thursday show that based on current migrant entries and a 'technical assumption' about future flows, arrival rates are unlikely to slow before 2017.

The EU's executive Commission said that 'overall, an additional 3 million persons is assumed to arrive in the EU over the forecast period.'

The refugees and migrants rescued off the coast of Libya gathered on the 'Canarias' frigate which then headed to the Italian port of Lampedusa

Greek Prime Minister Alexis Tsipras, left, and European parliament President Martin Schulz visit the Moria Hot Spot in Mytilene, Lesbos on Thursday

On Thursday, Greek Prime Minister Alexis Tsipras was a first-hand witness, seeing migrants and refugees reaching the Greek island of Lesbos by dinghy as his motorcade traveled from Lesbos airport to a new registration facility.

'We realized that is a criminal process being carried out by the smugglers who cram refugees onto vessels that are not boats, but makeshift inflatables,' he said. 'What's happening in the Aegean Sea is a crime.'

The flow of migrants into Greece's mainland and beyond was turning to a trickle on Thursday, however, as a ferry strike entered its fourth day and trapped thousands of people on the eastern Aegean islands.

Police in the Idomeni border area said 850 people had crossed into Macedonia between Wednesday and Thursday morning. Numbers usually range from 4,000 to 8,000 people per day.

The European Commission said the refugee crisis has resulted in additional government spending but that it could have a small, positive impact on European economies within a few years.

However the EU said the real impact on national budgets is difficult to predict, given a lack of complete and reliable data about exactly who is arriving in the bloc and whether they are staying.

A boy carries a can of water near a beach from where migrants are traveling by dinghies to the Greek island of Chios from Turkish coast near Cesme, Izmir, Turkey

Migrants queue to board a train on the way to Slovenia at a makeshift train station within a temporary camp in Slavonski Brod, Croatia

A Syrian woman carries her son at their arrival to a makeshift train station within a temporary camp in Slavonski Brod, Croatia, Wednesday Nov. 4, 2015. The weather is getting colder and many migrants are not equipped to cope with prolonged periods without shelter. (AP/Manu Brabo)

Most people are arriving in Europe through Italy and Greece, while Hungary and Austria have been affected by heavy migrant flows. Germany and Sweden are also feeling the impact.

Those nations, among others, want the EU to apply its budget rules with flexibility, taking into account Europe's biggest refugee emergency in well over half a century, and avoid reprimanding member states for excessive spending and deficits.

The Commission said Thursday that Sweden, which has the highest share of refugees per capita, is likely to feel the economic impact most, perhaps 0.5 percent of its gross domestic product this year.

Other hard-hit migrant transit and destination countries are likely to see an impact of 0.2 percent of their GDPs in 2015.

While acknowledging the potential short-term impact, the Commission did not clearly state whether it would be flexible on budget policy.

However a senior EU official said on Wednesday that some flexibility might be allowed 'taking into account well-specified costs and for a limited period of time.'

'This has been an asymmetrical shock for some member states,' said the official, briefing reporters on condition that he not be named.

As long as any help is 'one-off, shortish-term,' members of the euro single currency bloc would agree to it, he said.

Also on Thursday, Britain's Secretary of State for the Department for International Development Justine Greening claimed that Europe was likely to be mired in a migrant crisis for the next two decades.

Ms Greening's alarming estimate comes as the conflict in Syria and further turmoil in the Middle East show no signs of abating.

"In the 1980s, the typical time that someone spent as a refugee from conflict was about eight years, whereas today that estimate is around 20 years," Ms Greening said.