Interest in Finland's bomb-proof bunkers has rocketed as European countries prepare to re-arm amid a mounting risk of war. The Nordic country, which shares a border with Russia, has underground facilities said to be able to shelter nearly all its citizens.

Public facilities including swimming pools and amusement parks also serve as air raid bunkers in Finland, which has a reported 50,500 civil defence shelters. These have room enough for 4.8 million people, out of a population of 5.6 million.

The Itakeskus water park is one such shelter. Built metres underground, the park's pools can be emptied and turned into bomb-proof shelters in three days, with space for 3,800 people.

Teemu Raatikainen, the park's maintenance chief, told the AFP news agency: "This is the largest civil protection shelter in the world equipped with a pool."

After Russia launched its full-scale invasion of Ukraine in February 2022, interest in Finland's shelters has increased.

Another shelter in the middle of the Finnish capital, Helsinki, has space for 6,000 people.

By day, Merihaka is an underground children's playground and includes sports courts and a gym. But in the event of an attack, it can be converted into a place of relative safety for thousands.

Jarkko Hayrinen, senior rescue officer at Finland's Ministry of the Interior, hailed the country's multipurpose shelters.

He said the shelters are "well maintained" because people use them during "normal" times.

Ukraine's President Volodymyr Zelensky is among those who have taken an interest in Finland's bunkers, having toured Merihaka.

King Frederik X and Queen Mary of Denmark also visited the Merihaka civil defence shelter in March this year.

Mr Hayrinen said Finland first legislated for shelter construction in 1939, two weeks before the Winter War with Russia began.

The Winter War was fought between Finland and the Soviet Union after the Soviets invaded just months after the outbreak of the Second World War.

Finland's rescue expert said at that time the country wasn't prepared to defend its people in wartime, adding: "It was a harsh lesson for us."

More than 80 years later and the Nordic country has almost enough shelters for all its people.

These are designed to withstand radiation, toxic gases, explosions and collapsing buildings. With Russia and Finland sharing a 832 mile (1,340km) border, the EU country occupies a strategically difficult position.

In the aftermath of Russia's invasion, Finland joined the NATO military alliance, just a few weeks ahead of its neighbour Sweden.

Helsinki announced at the beginning of April that it would boost its defence spending to at least 3% of its gross domestic product by 2029 as it continues to respond to the security threat posed by Vladimir Putin's Russia.