As the two cooling towers at Belgium's Doel nuclear power belch thick white steam into a wintry sky, people over the border in the Dutch town of Nieuw-Namen are on edge.

They are part of a groundswell of concern in the Netherlands, Germany and Luxembourg over the safety of Belgium's seven ageing reactors at Doel and at Tihange, further to the south and east.

"I'm happy Holland, Germany and Luxembourg are reacting because they (officials) don't listen to you and me," butcher Filip van Vlierberge told AFP at his shop in Nieuw-Namen, where people can see the Doel plant.

Benedicte, one of his customers, nodded in agreement.

Van Vlierberge said he was particularly uneasy with the Belgian government's decision in December to extend the lives of 40-year-old reactors Doel 1 and Doel 2 until 2025 under a deal to preserve jobs and invest in the transition to cleaner energy.

"I'm concerned they are too old," he said.

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

Luxembourg's sustainable development minister Camille Gira is due in Belgium on Monday to raise his concerns.

Then Dutch Environment and Infrastructure Minister Melanie Schultz will visit Doel with Belgian Interior Minister Jan Jambon for a joint inspection on Wednesday.

- Unsolved sabotage -

Doel 1, the country's oldest reactor, was originally shuttered in February 2015 under a law calling for the country's gradual phaseout of nuclear power, but the government then restarted it under the extension deal.

But the plant, about 15 kilometres (nine miles) as the crow flies from the major port city of Antwerp, had to be closed three days later due to a generator problem. It has now restarted a second time.

Meanwhile Belgian operator Electrabel said in December it had restarted a reactor at its Tihange plant, just days after being forced to shut it down following a fire in the electricity supply system.

Tiny cracks discovered in 2012 in the reactor pressure vessels of Doel 3 and Tihange 2 caused lengthy closures of those two reactors. They were both restarted at the end of last year, one having to close quickly again, for a few days, after a water leak.

And the Doel 4 reactor was also shut down urgently in August 2014 after a leak in the turbine hall, caused by tampering, gushed out 65,000 litres of oil lubricant.

Belgian prosecutors told AFP the investigation into who was responsible is continuing, and they do not rule out terrorism or an "act of vengeance".

Peter, a Dutch docker returning from work in Antwerp, was especially worried about the unsolved sabotage case.

"I don't understand how such things can happen," Peter told AFP in Nieuw-Namen, adding that "people are a little afraid" over the range of reactor problems.

Germany's environment minister Barbara Hendricks in the past week sent a set of safety questions, including on the cracks, to the Belgian nuclear watchdog AFCN, which maintains all reactors are safe.

Both Electrabel and AFCN said the recent problems have only been in the non-nuclear parts of the reactor and there is no danger from the nuclear cores despite the microcracks.

"We resumed service following an audit from a US research firm, an international firm that guaranteed the structural integrity of the vessels," Electrabel spokeswoman Florence Coppenolle told AFP when asked about the cracks.

- Fukushima, Chernobyl ghosts -

But Eloi Glorieux, Greenpeace's nuclear campaigner for Belgium, insists the microcracks in the Doel 3 and Tihange 2 pressure vessels are cause for concern because they are "one of the most vulnerable parts" of the plant.

"If the reactor pressure (vessel) fails, then we have a Chernobyl and a Fukushima-type accident," he warned.

In March 2011, an earthquake and tsunami in Japan triggered meltdowns at the Fukushima plant, the world's worst nuclear disaster since Chernobyl in Ukraine 25 years earlier.

It was Fukushima that persuaded Germany to phase out its own nuclear plants.

Glorieux warned that any catastrophe in Belgium would be far worse than in Fukushima or Chernobyl, because its plants are near such densely populated areas.

Tihange is 20 kilometres from the Belgian city of Liege, 40 kilometres from the Dutch city of Maastricht and 60 kilometres from the Germany city of Aachen.

The authorities in Maastricht and Aachen have hired lawyers to consider possible legal action against Belgium to ensure plant safety, or even make them close down.

Electrabel's Coppenolle said the criticism of Belgium was misdirected as the Dutch have extended by 20 years the lifespan of their reactor on the Belgian border until 2033 while nine German reactors will run until 2022.