Finland uses the same track widths as Russia, which are wider than the European standard - a holdover from when the Nordic nation was part of the Russian Grand Duchy in the 19th and early 20th centuries.

It is currently in the process of updating its track widths to match the European standard.

The new, twice-daily journey to Sweden's Haparanda takes 100-minutes as it hugs the west coast of Finland before crossing the border between the two Nordic neighbours.

Passengers travelling on from Haparanda will need to transfer onto a different train to continue southward.

But the service makes it possible to travel around 5,000km by rail from Portugal's Algarve to Finland's northernmost train station of Kolari - believed to be the longest train route in Europe.

It will also enable a 24-hour train journey between capitals Helsinki and Stockholm.

Finland's transport minister said the return of the cross-border service shows cooperation between the two countries was growing "all the time".

Elisa Markula, chief executive of Finland's state-owned railway operator VR, said she hopes the service will benefit from a "renaissance" in rail travel across Europe.

"Train travelling in all Europe is having a renaissance. Also in Finland, our passenger numbers are increasing a lot," Markula told AFP.