The Dutch government has ordered 15 million iodine pills to protect people living near nuclear plants in case of an accident, officials said Friday, as concerns rise over ageing reactors across the border in Belgium.

The iodine pills, which help reduce radiation build-up in the thyroid, would be given to children under 18 and pregnant women living within a 100-kilometre (62-mile) radius of a plant, health ministry spokeswoman Edith Schippers told AFP.

Until now, the tablets have been available within 20 kilometres of a plant, to everyone aged 40 and under.

The Netherlands has only one nuclear power plant -- at Borssele in the southwest -- but the expansion will also see pills given to people living in border areas near Germany's Emsland plant and two Belgian facilities, Doel and Tihange.

The Dutch announcement came a day after Belgium announced it planned to distribute iodine pills to its entire population of 11 million people in case of a nuclear accident, with the details to be decided in 2017.

Dutch authorities said they would "follow how (the Belgians) carry out the distribution of these pills and where they will be available -- whether people will have to go and find them at a pharmacy or at a local health service," Schippers said.

Once tablets were distributed to children and pregnant women, the rest of the supply of 15 million could be made available to everyone caught up in a potential accident, including "tourists, visitors and workers".

Belgium's creaking nuclear plants have been causing safety concerns for some time after a series of problems ranging from leaks to cracks and an unsolved sabotage incident.

Security fears have also risen after investigators last year discovered surveillance footage of a Belgian nuclear official in the apartment of a suspect linked to the Brussels and Paris attacks.

Last week Germany asked that the 40-year-old Tihange 2 and Doel 3 reactors be turned off "until the resolution of outstanding security issues", which Belgium rejected, saying the plants were subject to "the strictest possible safety requirements".