Finland began constructing the fence, which will eventually cover 200km of the border's total 1344km length, last year in response to migration via Russia through the border in 2023, which it believes was deliberately orchestrated by the Kremlin.
"The main purpose of the fence is to control a large mass of people if they are trying to enter from Russia to Finland," the deputy commander of Southeast Finland Border Guard District, Antti Virta, told Reuters.
In Nuijamaa, near one of the closed border crossing points, the scene is tranquil, with just the sound of birdsong to be heard on both sides of the new fence on Wednesday.
But Finland has faced criticism, and not just from Russia, over the border closure and fence construction.
After decades of peaceful relations with Russia, Finland joined the NATO military alliance two years ago in response to Russia's invasion of Ukraine, prompting the Kremlin to threaten Finland with retaliation.
The same year - in 2023 - about 1300 migrants from third countries such as Syria and Somalia arrived via Russia at the Finnish border to ask for asylum, until Finland closed all eight passenger crossing points to Russia indefinitely to put an end to the phenomenon.
Russia has denied orchestrating the migrant flows.
At the time, the Russian government said it deeply regretted Finland's decision to shut crossings on its border, saying it reflected Finland's adoption of an anti-Russian stance.
Virtually no migrants arrived after Finland closed the border for passengers at the end of 2023 but the Border Guard defended the decision to build the fence.
"The border barrier is absolutely necessary to maintain border security," Head of Operations Samuel Siljanen said.
"From the Border Guard's perspective, it improves our ability to perform border surveillance, to act if there's some kind of disruption at the border or a border incident," he said, adding that the fence was needed to combat orchestrated migration.
The European Court of Human Rights has asked Finland to justify the indefinite closure of the border.
The Council of Europe Commissioner for Human Rights, Michael O'Flaherty, last year warned that Finland's temporary restrictions on asylum applications "would violate international obligations, including the prohibition of refoulement and collective expulsion".
The fence consists of 3.5-metre high metal railings topped with a metre-high roll of barbed wire and it is equipped with cameras, sensors, loudspeakers and lights.
It will be completed by the end of 2026, the Border Guard said.
