Swiss border guards recorded 16,563 cases of illegal migration last year, down from 27,300 cases in 2017 and 48,838 in 2016.
Most of those without valid papers were stopped in southern Switzerland: 4,832 in canton Ticino and 3,122 in canton Valais.
Regarding nationality, 2,433 people were from Nigeria, 1,176 from Gambia, 803 from Algeria, 792 from Morocco, 685 from Albania and 663 from Eritrea.
The previous year’s list was headed by people from Guinea, Nigeria and Gambia. In 2016, some 12,294 people had travelled from Eritrea alone.