Officials have announced a 10-year, £17 million project to prevent the collapse of the medieval Garisenda Tower – one of the two towers that look out over central Bologna.

Like the more famous Leaning Tower of Pisa, it has leaned for centuries as the ground on which it was built gave way soon after construction. The area around it was cordoned off last month because of rising concerns among experts about the risk of collapse.

The Garisenda slants at 4 degrees, compared with 3.9 degrees for the more famous Leaning Tower of Pisa.

“I think we will spend no less than €20m, maybe more” to restore and consolidate the tower, Bologna’s mayor, Matteo Lepore, was quoted by the Ansa news agency as saying in a press conference at city hall.

“For the tower of Pisa, it took 10 years for the intervention and the [restoration] project. We have no reason to say it will take us less,” he said.

The 12th-century Garisenda is 48-metres high and stands next to the taller Asinelli (97 metres). The much-loved landmark is cited several times in Dante’s Divine Comedy and Le Rime, and Charles Dickens wrote about it in his Pictures from Italy. The Garisenda was also referred to in Goethe’s Italian Journey.

Italy’s civil protection agency has put out a yellow alert for the area around the two towers, meaning it is under watch but thought to pose no immediate risks to people’s safety. There are two possible higher alert levels, orange and red.

Work to reinforce both towers has been ongoing since the 1990s. Preliminary work on the Garisenda Tower would include creating a containment area to prevent any damage to nearby structures or harm to passersby from a “possible collapse”, the city said in a statement. Video cameras will maintain surveillance of the site.

The Garisenda and Asinelli towers are named after the rival families who built them, believed to have been a way to compete over their power and wealth, and are located at what was the entrance to the city. The Garisenda was originally 60 metres tall but had to be lowered after it began to lean.