Leading French architects have attacked the planned glass renovation of the Gare du Nord rail station in Paris, warning that the project to create a vast shopping space is “unacceptable”, “indecent” and a “serious offence to transport users”.

The award-winning French architect Jean Nouvel as well as historians and town planners wrote an open letter to Le Monde saying the €600m (£540m) renovation plan to create a glass structure – with tens of thousands of square metres of shops, walkways, split-levels and 105 escalators – was a “serious urban error” that would deform the historic building, fail Parisians and befuddle travellers.

The station in the north of Paris is Europe’s biggest rail hub, with 700,000 passengers a day – including those arriving from London on the Eurostar and 500,000 local passengers who use trains connecting the Paris suburbs.

For years, the 19th-century building has suffered from unflattering comparisons with the gleaming St Pancras in London where Eurostar passengers alight in the UK. Andy Street, the former head of John Lewis who is mayor of the West Midlands, even had to apologise to France in 2014 after calling the Gare du Nord “the squalor pit of Europe” compared with what he called the “modern, forward-looking” St Pancras.

Although France has spent millions on small-scale changes to the Gare du Nord in recent years, rail authorities warning the nation’s “image was at stake” have joined with a major private commercial shopping centre investor to triple the station’s surface area and overhaul the site before the Paris Olympics in 2024.

“This project is unacceptable and we demand a rethink from floor to rafters,” the protesting architects wrote in Le Monde, adding that it was indecent to send travellers up and down a mess of walkways, lifts and escalators, forcing them past shops to reach their platforms. They said that the vast volumes of the “beautiful” train hall would be “denatured” by adding high walkways. They warned of committing a “serious urban error” in the form of a giant shopping centre that risked killing smaller local trade in the Paris region.

The renovation will include working spaces – which some have suggested would allow companies to relocate from the UK after Brexit but stay close to the Eurostar – as well as a running track on the roof with views over Paris. A new Eurostar area will provide more space for customs checks after Brexit.

The aim is to have the station ready by the Paris Olympics in 2024, but work must take place while the Gare du Nord remains open to passengers – a complex process.

The architects said it was “ridiculous” to think the colossal project could be finished by 2024.

Green politicians in Paris have also complained about the plans and one local oversight body recently ruled against planning permission. But the Gare du Nord development team saw this as a minor hiccup. They will appeal and fully intend the work to go ahead.