Greenpeace activists broke into the grounds of nuclear plants in six European countries Wednesday, urging governments to close down ageing reactors on safety grounds.

Protesters dressed in orange jumpsuits scaled boundary fences at plants in France, Belgium, the Netherlands, Switzerland, Sweden and Spain and hoisted large banners with images of cracking reactors and projected the words "The End" onto walls.

Some 240 activists took part, said Greenpeace, urging governments in a statement to "invest instead in clean and safe energy".

Of the 151 reactors in Europe, 66 are older than 30 years, 25 older than 35, and seven over 40, the environmental group said.

The lives of many had already been stretched beyond their initially-intended span, it added.

"The majority is threatening to overshoot their technical design life-time," said Greenpeace nuclear energy spokesman Jan Haverkamp, pointing to the March 2011 disaster at Japan's Fukushima plant, which started operating in 1971.

"The increasing age of the reactors also increases the risks for a nuclear incident and significant economic and environmental damage."

In northern France, 18 protesters entered the Gravelines power plant, which will turn 40 in 2020, at dawn, said Greenpeace.

They claimed to have crossed three security barriers and were approaching reactor No. 6 when they were apprehended.

France's interior ministry insisted the group was arrested within eight minutes of setting foot on the premises, and said their movements were followed from the start.

In Belgium, some 60 activists entered the grounds of the Tihange reactor 80 kilometres (50 miles) southeast of Brussels, and projected the words "The End" onto one of the chimneys, Greenpeace claimed.

Protesters in Borssele in the southern Netherlands also used a film projector to display the message onto a reactor which was built to last 40 years but has been given another 20-year lease on life.

Twenty-odd protesters in southern Sweden climbed over the fence around the Oskarshamn reactor and erected a banner stating "Time for retirement".

Police told the local news agency TT that 13 activists were arrested for trespassing at the reactor -- built in 1972 and initially due to last for 40 years.

Several safety scares had forced its temporary closure in recent years.

Banners announcing "The End" of nuclear power were also erected at the 45-year-old Beznau nuclear plant in northern Sweden, while in Spain, about 30 activists with construction vehicles reenacted the dismantling of the Garona plant erected in 1971.

A dozen protesters used trucks to block the entrance to the Bugey nuclear station in eastern France, which will turn 40 in 2018.