Hungarian police said Friday that they discovered two tunnels used by migrants to enter the country from Serbia.
Police said that a tunnel 34 meters (37 yards) long was discovered near the southern village of Asotthalom, where they also detained 44 migrants who had used the precarious passageway.
Police Col. Jeno Szilassi-Horvath said a Serbian citizen suspected of human trafficking had been detained along with the migrants.
The tunnel near Asotthalom was about 50 centimeters (20 inches) wide, 60 centimeters (2 feet) high, and had been dug as deep as about 6 meters (20 feet) below the surface without any support beams or other elements to prevent its collapse.
Szilassi-Horvath said the dig, which likely lasted a few weeks and was done without any machines, had gone undetected thanks to the thick underbrush in the area and because the soil dug out was dumped in a nearby canal.
He added that security officials were using drones and scanners to search for any more tunnels.
The other tunnel, in the village of Csikeria, was 21.7 meters (71 feet) long, but no successful migrant crossings took place there. Police said they discovered both tunnels not long after their construction was completed, and filled both of them up again.
In 2015, at the height of the migration crisis, Hungary built razor-wire fences on its southern borders to stem or divert the flow of people, many from the Middle East and Asia, making their way to Western Europe.
In recent weeks, the number of migrants found near the border in Hungary and expelled back to Serbia through gates in the fences has been on the rise, from usually far less than 200 a week earlier this year to 375, 492 and 642 in the past three weeks.
Asylum-seekers may file their claims at two transit zones along the border, but recent legal changes allow authorities to reject the vast majority of the claims of those arriving from Serbia.