Illegal migrant crossings into Europe were up by nearly 50 per cent in the first five months of 2021.
EU border agency Frontex said crossings were on the increase again after falling to a record low in the early months of the pandemic.
In May, with Covid restrictions reduced in much of Europe, the number of arrivals was more than double that in May 2020.
The total from January to May was 47,100, a rise of about 47 per cent compared with the same period last year.
The biggest jump took place on the central Mediterranean route from North Africa to Italy.
The number of illegal crossings on that route more than doubled compared with last year, with about 15,700 between January and May.
More than 1,000 boats arrived on the Italian island of Lampedusa in the space of 12 hours at the height of the influx in May, leading to fears for safety on the island. A police union official described the situation as "literally explosive".
Migrants from Tunisia and Bangladesh were the two largest groups taking the route.
In the Eastern Mediterranean, numbers were down compared with early 2020 when Turkey sparked a crisis by throwing open its border with Greece.
However, there was a threefold rise in May, when about 1,400 crossed into Europe on the route.
Frontex is under scrutiny by rights groups for its alleged role in forcing migrants back to Turkey, which it denies.
It has about 600 officers in Greece monitoring the border and dealing with incoming migrants.
Greece proposed last month that the border agency should operate beyond Europe's waters to stop illegal migrants.
More than a million refugees and migrants entered Greece at the height of the 2015 refugee crisis, mostly on boats from Turkey.
Most of the illegal crossings on the Eastern Mediterranean route this year were by Turkish and Syrian citizens.
More guards in Spain
Migrant crossings to Spain were also up compared with last year, with people from Algeria accounting for three quarters of these.
About 4,500 people crossed the Mediterranean to Spain, while another 5,300 arrived in the Canary Islands.
Frontex said it would increase its presence in Spain for the summer, with 100 officers checking arrivals at Spanish ports.
They will include forged document experts and border guards specially trained to detect stolen cars.
“The information collected during the operation is important for the fight against criminal organisations and future investigations,” Frontex said.
Some of the Frontex officers will be stationed at the Spanish enclave of Ceuta on the coast of North Africa.
Spain sent troops to the enclave last month after a sudden surge of migrants to the border.
About 1,500 migrant children are being housed in overcrowded warehouses in Ceuta, activists say.