Libya was the most popular departure point for illegal crossings into southern Europe last year, the European Border and Guard Agency said.
One-third of about 200,000 people who were stopped last year by coastal and border guards in European countries had arrived by crossing the Central Mediterranean.
The route runs from North Africa, primarily from Libya, to Italy.
Frontex, as the agency is called, said in its latest survey illegal immigration is up 83 per cent, year-on-year.
The UN’s refugee agency said the popularity of the route was unlikely to drop, owing to Libya’s proximity to Europe and that political instability in the country prevented an effective border force operation from being mounted.
Most of those using the route rely on unstable vessels and rickety boats to cross dangerous waters. They are often subject to exploitation by human traffickers.
The total number registered by Frontex in 2021 is the highest since 2017.
People migrating illegally or seeking refuge have seized on the relaxing of Covid-19 restrictions in many countries.
Up to 65,000 people have tried to reach Europe from Libya or Tunisia.
They were followed by nearly 60,000 from the Balkans, the report said.
The border authorities returned more than 18,000 citizens of non-EU states to 102 destination countries last year.
About one in 10 of all detected irregular crossings last year occurred on the Eastern Mediterranean route, from about 20,000 people. The Eastern Mediterranean route refers to arrivals from Turkey, Greece, Cyprus and Bulgaria.
Syrians remained the most frequently reported nationality of the people detected when crossing the border without permission, followed by Tunisians, Moroccans, Algerians and Afghans.
As in 2020, women continued to make up fewer than one in 10 arrivals in 2021, a significant drop in their share compared with that in 2019.
The Frontex data cover only people who tried to enter the EU illegally and were caught. There is no accurate information on the number of people who infiltrated the bloc.
But the International Organisation for Migration estimates that about 610,000 migrants, comprising more than 44 nationalities, are in Libya.
Many of them have escaped war and poverty elsewhere in Africa and hope to reach Europe by crossing the Mediterranean.
The UN has condemned the Libyan authorities for subjecting tens of thousands of migrants to appalling treatment including enslavement, torture and rape.
On Monday, UN Secretary General Antonio Guterres said more than 12,000 people were known to be held in 27 prisons and detention centres in Libya and that thousands more were being detained illegally.
To curb migration through the Mediterranean, EU countries, chiefly Italy, have signed agreements with Libyan officials to train and equip local coastguards.
Last year was one of the deadliest for illegal migration to Europe by sea or land, with at least 4,400 deaths, the IOM said.
The figure could be far higher because unseaworthy boats often sink without a trace.
A group of international human rights organisations, including Amnesty International and Human Rights Watch, said in a joint statement last year that the Central Mediterranean route is one of the most dangerous migration routes in the world.
“Many lives could be saved if EU member states ensured and enabled robust search and rescue operations in the Central Mediterranean. There’s no evidence that SAR operations encourage people to embark,” the statement said.
The first presidential election was due to take place in Libya on December 24, followed by legislative polls, but the UN-sponsored electoral process was postponed owing to political tension.