Police raids across Greece have smashed an international people trafficking ring that made $8 million in profit from smuggling Syrian migrants into Europe, and 16 suspects were arrested, officials said.

The operation served to "reinforce our actions against...the ruthless criminals who facilitate irregular migration to Europe through the Mediterranean Sea," said Dimitris Avramopoulos, European Union Commissioner for Migration and Home Affairs.

"We are confronted with an unprecedented increase in people embarking on dangerous journeys, to escape wars," he told reporters in The Hague, alluding in part to Syria's civil war, which has displaced about half the country's population.

Rob Wainwright, chief of the European police organisation Europol, said Greek authorities backed by the Netherlands-based Europol dismantled the gang in a two-day sweep last week, the first by a new Europol task force dealing with maritime crime.

He said police staged 20 raids across Greece, arresting 16 suspects - including Syrian, Iraqi, Egyptian and Romanian nationals - and seizing 280 passports, dozens of mobile phones, computers, vehicles and 64,000 euros ($68,000) in cash.

In 2014, more than 220,000 migrants entered Europe, compared to 60,000 a year earlier, and more than 4,000 have died since 2013 attempting the sea crossing, Wainwright said at a media briefing in The Hague.

He said the gang had smuggled 350 people, mostly Syrians, by boat to the Greek islands of Kos and Rhodes, charging as much as 9,000 euros ($9,500) per person, Europol said.

The EU's executive Commission is drafting a new immigration policy, due to be adopted in May, that would offer expanded opportunities for legal migration as a way of reducing a wave of illegal migrants from the Middle East and Africa.

The new Europol task force will bring together leading intelligence experts from European countries most affected by illegal migration. Working in The Hague, they will share key data and coordinate actions against human traffickers