Brandishing banners demanding "safe passage now" for migrants, some 3,000 marchers attended a rally in Brussels in support of people fleeing conflict and persecution, police said, while smaller demonstrations drew hundreds in Paris and other European cities.
Some marchers symbolically wore life jackets and blankets to highlight the perilous journeys of migrants refugees, notably from the Syrian conflict, in rickety vessels across the Aegean Sea to make it to Europe.
As European nations struggle to cope with the inflow, protesters insisted on refugees' right to safety.
"Nowhere is it written in the Geneva Conventions that one can close borders to refugees -- quite the contrary," the Belga news agency quoted one Brussels marcher, Beatrice Dispaux, as saying.
"These people need help and shelter and we can give them that. The situation is critical, the politicians must act urgently," she added.
Several rallies were held across Germany, a magnet for many of those seeking a new life in Europe, while a Belgian group of associations said on its website that some 100 cities across Europe and beyond were holding marches in support of migrants.
In central Paris some 200 protesters gathered, while marchers in the northern German city of Hamburg held aloft Afghan flags and banners reading "No nation, no border."
Balkan states along the migrant route taken by hundreds of thousands of people fleeing war and misery in the past year have recently shut their borders to Afghan nationals, allowing only Syrians and Iraqis to go through.
Rights groups including Amnesty International joined several of the rallies in Europe, along with several leftist groups.