Shanghai's heritage conservation authority is planning to repair an ancient tower that is tilting and needs reinforcement to keep from falling over.

Located in the city's suburban Songjiang district, the seven-floor octagonal tower was built in 1079 by a military general. According to local legend, it used to store sarira－bead-sized stones－that shone in the night. Hence, the tower is called Huzhu, which in Chinese means protecting pearls.

The tower, located in Tianma Mountain Park, is made of wood, mortar and bricks. It has been leaning toward the southeast and has undergone several restorations throughout its history.

According to a survey conducted in 1982, the tower, which is 18.8 meters high, tilted 6.5 degrees toward the southeast, about 2.27 meters from the axis. It's latest restoration occurred later that year to keep it from leaning further.

However, recent surveys have identified an increase in the tower's inclination, which was at 7.1 degrees in 2015, according to statistics from the municipal heritage conservation authority. In comparison, the inclination of Italy's Leaning Tower of Pisa is about 5 degrees.

Moreover, Songjiang Forestry Farm, the managing body of the tower, identified two new 50-centimeter cracks in the lower part of the tower and further sinking on the southwest side of its foundation during recent inspections.

While the tower's conservation has been approved by the municipal administration of culture and tourism, the detailed plan is still being worked on, according to the Songjiang District Heritage Preservation Management Office, which is in charge of the restoration project.

The principle of the project is "not to alter the raw condition of the heritage", and the restoration will be minimally invasive, the office said.

According to Yang Jiayou, an architect who participated in the previous restoration project, an unsteady foundation is part of the reason the tower tilts.

"The tower stands on the slope of a hill, and the density of the soil underground is different－one side is harder and the other softer, and therefore the tower tilts," Yang was quoted as saying in a previous interview.

Yet the tower remains sturdy enough to stand thanks to the mixed use of glutenous rice, limestone powder and tung oil to glue bricks in ancient masonry and its octagonal structure.

The tower survived a fire during the Qing Dynasty (1664-1911), which destroyed its wooden stairs and floors. Only the brick shell of the tower remains.