People-smuggling gangs netted up to 6 billion euros ($6.6 billion) last year, most of it from the traffic of migrants into Europe, the European Union's police agency Europol said in a report issued on Monday.
Labeling people-smuggling as the "fastest growing criminal market in Europe", the report said: "This turnover (of 6 billion euros) is set to double or triple if the scale of the current migration crisis persists in the upcoming year."
Europol and police forces in countries in Europe and beyond have identified more than 12,000 suspects active in gangs involved in smuggling in migrants since 2015.
Gangs, whose members come from countries including Bulgaria, Egypt, Hungary, Iraq and Kosovo, are engaged in a huge range of criminal activities including document forgery and official bribery, the report said.
So-called "hotspots" where gang activities is concentrated include cities along the Balkan route from the Middle East, such as Istanbul, Izmir, Athens and Budapest, as well as major continental hubs like Berlin, Calais, Zeebrugge and Frankfurt.
But Europol said there was little evidence that "terrorist suspects" were making use of migrant smuggling networks to enter the continent on a significant scale.
"Far less than 0.01 percent of terrorist suspects have had migrant links," said Europol director Rob Wainwright at a news conference.
About one million migrants reached Europe last year, most of them fleeing war and poverty in the Middle East, the agency said in a report issued as it set up a new center to coordinate the Europe-wide fight against the smugglers.
The European Migrant Smuggling Centre, which will be based at Europol's headquarters in The Hague, will help police forces in and outside Europe share intelligence and will help with rapid deployment of emergency police forces as new migrant routes emerge.