Tourists travelling to visit historic French landmarks the Eiffel Tower and Normandy's Mont Saint Michel have found their doors closed for part of the past two weeks, as striking workers complain of underinvestment and too many visitors.

Investment in Mont Saint Michel, a fortified tidal island topped by an abbey, is "not at an appropriate level for this fantastic monument", one staff representative said.

And an Eiffel Tower unionist last week warned that the cost of "major maintenance, renovation and conservation work" is being "underestimated" at the 125-year-old iron structure.

In Normandy, Herminia Amador Chacon of the CGT union said Mont Saint Michel workers "all have joint problems in the knees or the ankles" from staffing and guiding visitors around the site, which is accessible only by climbing 350 stairs.

Others are posted out in the wet, rainy Channel weather for hours on end, with one reception worker calling the spot "marvellous but badly heated".

Only around 15 of the Mont Saint Michel's 55 workers have walked out since the open-ended strike began on December 26.

But that has been enough to shut the gates of the abbey — one of France's most visited monuments, with around 1.5 million tourists per year — many days since.

Lise, 25, and Thomas, 24, had travelled the 70 kilometres (43 miles) from Norman town Flers to visit on Wednesday, only to find a sign saying the abbey was only open between 1:00 pm and 5:00 pm.

While "a little disappointed", the pair judged the staff could not "be on strike over nothing".

Worker representatives at Mont Saint Michel are asking for more staff, extra pay for those with foreign language skills and compensation for the physically demanding parts of the job, as well as better facilities on site.

Abbey general secretary Arnaud Noblet said extra staff were already on hand during the busy summer season and a small number of new jobs were being created.

He dismissed the idea that spending on the abbey was not in line with revenues.

Pooling of resources among landmarks managed by the Centre for National Monuments (CMN) authority means "major monuments like the abbey keep the small ones alive", Noblet said.

Eiffel Tower 'heading for disaster'

In Paris, strikers among the Eiffel Tower's 360-strong workforce said they had walked out for one day on December 27 to protest against "unrealistic management" with "over-ambitious, impossible-to-achieve" business goals.

"The Eiffel Tower is an old lady. It's 130 years old. Some of the lifts date back to 1899. There's a lot of work (to be done)," the workers said.

They added that managers' projections of 7.4 million visitors per year were unrealistic — the tower hosted 5.9 million in 2022 — leaving a funding gap that workers believe has management firm SETE "heading for disaster".

But SETE boss Jean-Francois Martins said the Eiffel Tower was "in good economic shape", even after the Covid-19 pandemic and inflation hit renovation costs.

He said he believed workers fear jobs could be cut to make up for pandemic-era losses.

Italian tourist Alessandro Monaco, 40, was disappointed.

"We were quite stunned to see there was a strike. It's a real shame not to be able to visit today," he told AFP on the day of the stoppage last week.

Others were more sanguine.

"The important thing is to see it, strike or no strike," said 40-year-old French visitor Marie-Christine Riviere.

While the Eiffel Tower strike on December 27 lasted for just one day, "if the situation continues… the Eiffel Tower will be closed during the Olympic Games period" in July-August, worker representatives warned.