Tuesday’s discovery was made by a technician from Enedis, which manages the electricity distribution network in France, who was working “in a well for electrical connections” around 450 metres away from the La Sante Prison, a police source said.

“Bags of rubble and a bed” had been found at the scene, the source added.

Guillaume Durand, an official with the town hall of the French capital’s 14th district, where the prison is located, said he doubted an elaborate escape plan had been in the works.

“It’s a four-metre tunnel, in a cul-de-sac on rue de la Sante, but more than 500 metres from the prison,” he said.

“Police believe that it is rather something which would aim to facilitate the arrival at the catacombs, therefore the work of cataphiles,” he said, referring to clandestine catacomb explorers.

He said officials had sent an engineer to the site to fill in the hole.

The Paris Catacombs, the massive underground ossuary, are one of the city’s most popular attractions and lure some 500,000 visitors a year.