The Palace of Heavenly Purity in the Forbidden City Photo: CFP

The Forbidden City will more than double in size for tourists when renovations are completed in 2020, a cultural heritage official announced Wednesday.

To relieve congestion and protect cultural relics, the area accessible to visitors is being expanded from 30 to 70 percent of the total palace complex.

Those were the figures declared by Shan Jixiang, director of the State Administration of Cultural Heritage, at the Fifth Beijing Park Festival in the Summer Palace.

The 30 percent of the Forbidden City open to the public - an area of about 216,000 square meters - has an ideal capacity of 30,000 people a day, Shan said. The actual number in extreme cases has been 130,000, with corrosive damage being left on the former home to 24 emperors.

Allowing tourists to visit more of the Forbidden City was a useful means of relieving the pressure, said He Shuzhong, chairman of the Beijing Cultural Heritage Protection Center.

"Endless foot treading makes the stone floor bumpy," he said. "All that breathed-out air generated by massive numbers of tourists corrodes the buildings. Plus some tourists carve on the relics.

"But it's difficult to limit the number of tourists. Because the Forbidden City is a place every Chinese dreams about next to Tiananmen Square as a must-see."

Ongoing renovations to the imperial palace respect the original design, according to Shan, and the materials and technology used were selected to preserve as much historical detail as possible.

Authorities have for example installed floorboards and covers over the original floor and pillar bases of the newly renovated Wild Goose Wing Towers.

Visitors on June 28 spotted a "was here" scrawled on a horizontal calligraphy-inscribed board, 30 meters up on the Hall of Preserving Harmony. Luckily the board had not been permanently harmed by the graffiti.

A six-year renovation process opened in 2002 with an annual budget of about 100 million yuan ($14.73 million), the Sanlian Life Weekly magazine reported in 2004.

The budget will be recalculated for the 2008-2020 phase two renovation.

The Forbidden City famously has 9,999 rooms, but the area open to tourists is far fewer and concentrated along the central axes of the Forbidden City.