TAIYUAN - Renovation on a heavily-damaged wooden pagoda, believed to be the oldest and tallest of its kind in the world, began on Thursday after two decades of delays.

Restorers plan to reinforce the 958-year-old pagoda, located in Yingxian County, north China's Shanxi Province, as the tower leans northeast. Several sections of the pagoda's wood, which has become rotten due to centuries of erosion, will also be repaired according to the provincial cultural heritage administration.

With a budget of 7 million yuan ($1.14 million), the revamp is expected to be completed within 18 months.

The 67-meter-tall pagoda was built with brackets and sockets, without nails. Visitors have been prevented from climbing to the second floor of the five-tier tower due to its poor condition.

While experts have long been concerned that the tower is on the brink of collapse, its revamp plan was only approved by the State Administration of Cultural Heritage this year.

The plan, which was initiated in 1989, was subject to lengthy reviews under professionals and authorities over the past years. There has been no meaningful action taken because of financial issues, practical difficulties as well as concerns on how alterations may be read by UNESCO.

In 2012, the structure was put on a tentative list of sites applying for UNESCO World Heritage status. Shanxi provincial authorities feared the revamp will destroy its "originality," one criteria in applying.