Finland's prime minister said on Tuesday the country will shut its last border crossing to Russia, following an influx of migrants which Helsinki claims is a hybrid attack orchestrated by Moscow.

Interior Minister Mari Rantanen said the closure would come into effect overnight between Wednesday and Thursday and last until December 13.

The Nordic country, which shares a 1,340-kilometre border with Russia, has seen a surge in undocumented migrants seek asylum on its border with Russia in November.

From the start of August, nearly 1,000 migrants have entered Finland without a visa through the eastern border crossing points.

"Finland is the target of a Russian hybrid operation. This is a matter of national security," Rantanen said.

Last week, Finland's northernmost eastern border crossing, Raja-Jooseppi, became the sole entry point to Russia, following the closure of the other seven transit points by the Nordic country.

Asylum seekers will be limited to apply for protection at "open border crossing points for air and maritime traffic," meaning ports and airports, according to a government statement.

"This is an organised activity, not a genuine emergency," Prime Minister Petteri Orpo said of the surge.

He added that the "ease with which the migrants found their way to the remote border crossing point at Raja-Jooseppi is also evidence of this."

"It is not just the number of arrivals that is at issue, but the phenomenon itself," Orpo said.

Finland's relations with its eastern neighbour soured after the start of the war in Ukraine.

After Finland acceded to the US-led military alliance Nato in April, reversing its decades-long policy of military non-alignment, Russia warned of "countermeasures." (AFP)