The migrants crossed the border at the Briģu parish over River Pernovka. In 2015 a total 12 people were detained here and 26 last year. Most of them were Vietnamese.
Uldis Grebežs, head of the region's Border Guard forces, said that the foreigners were detained following a tip from the locals.
They are now facing criminal charges and are being interrogated.
There's a 12-meter wide border strip at Opoļi, and an 8-km fence will be built there this year.
Last year 369 people were detained over crossing the border illegally. Some of them end up in Latvia's prisons facing criminal charges.
It is hoped that the number will reduce as preventive measures are increasing to deter people from choosing to try to cross Latvia's borders illegally.