The period of construction was a very interesting time, as Tornio became an international city during the First World War. From 1914 onwards, the city saw a huge influx of refugees, as Finland, along with Russia, was declared under martial law at the end of July. After the declaration of martial law, the citizens of Russia's enemies Germany and Austria-Hungary were given three days to leave the country. After the end of shipping in the Baltic Sea, the war left Tornio as the only route to the West, so Germans living in Russia and some Communist leaders, for example, headed for the border town.

During the first two weeks of the war, as many as 30,000 refugees passed through Tornio, and in 1915 some 120,000 people crossed the border in Karungi alone. Later, Tornio played an important role in the return of some refugees to Russia. The most famous of them was Lenin in 1917, who travelled from Switzerland via Tornio towards St Petersburg to make the revolution.

In the First World War, the losses and casualties were enormous on both sides. In total, more than 75,000 Russian, Austro-Hungarian, German or Turkish soldiers passed through Tornio, their severe injuries making them an additional burden on the prison camps of all sides. Tornio-Haaparanta was chosen as a prisoner exchange point because Sweden was a neutral country. The initiative was taken by the Red Cross.

Tornio also played an important role in the Jääkäriliike, when from 1915 Finnish men were sent to Germany for military training. In the Finnish Civil War, the Jääkärit formed the vanguard of the White Army, some of whom still played an important role in the Second World War.