Firefighters in Sicily have rescued about 400 rare books from a library in Niscemi that hangs on the edge of a mudflow, after a devastating landslide in January tore away an entire slope of the town and carved a 4km chasm.

The library stands on the lip of the precipice gouged out by the landslide, with part of the building in effect hanging in mid-air. The recovery operation, which began on Monday, was preceded by a detailed study of floor plans and interior photographs to map the position of the books.

Firefighters drilled through the wall of a building behind the structure and entering for minutes at a time, strapped the bookcases together and hauled them backwards to reach the books.

The library holds about 4,000 books of literature, history and general nonfiction, including a number of rare editions dating from before 1830 on Sicilian history. Among its most precious treasures is a 16th-century book.

“It was like pulling off a bank heist,” said Salvatore Cantale, the provincial commander of the fire brigade in Caltanissetta. “We had to be quick and try to take away as much as we could.”

A drone streamed live aerial images to a monitor on the ground, while laser sensors fixed to the section teetering over the drop were used to detect the slightest movement. A separate device monitored vibrations and subtle shifts in the building’s tilt.

The landslide began on 25 January when the ground started to shift, cracking asphalt and tearing through buildings. Some later collapsed into the void, along with a stretch of road where cars and vans had been parked. More than 1,600 people have been evacuated from the town.

Many of the volumes remain in the basement, which is considered the most at-risk area. Officials are weighing up the use of robots, though none suitable are available in Niscemi.

“If we can find the robot, we’ll use it immediately. Otherwise, we’ll have to wait,” Cantale said. “The problem is that this building is effectively a single reinforced-concrete structure. If it collapses, it will go all at once.”

Cantale said the geologists working next to the firefighters expected the landslide’s front to retreat by another 10 to 15 metres, dragging further buildings down the slope with it, including the library.

He said: “According to the geologists, rather than crumbling, the library is more likely to slide downhill as a single block. If that happens, we have already assessed that it may actually be easier to recover the remaining books once it has fallen.”

Some of Italy’s most famous writers had urged authorities to recover the collection, which lies in the “black zone”.

Stefania Auci, the author of the bestselling novel The Florios of Sicily, told the news agency Adnkronos: “I don’t know whether our appeal truly helped ensure that some of those ancient volumes were saved, but I like to think it played at least a small part.”