For example, in Jinan, capital of Shandong province, a German architect helped build a railway station in 1908. The Gothic-style structure was long used as the main transportation hub of the city and carried generations of local citizens' collective memory. It was demolished amid a huge controversy in 1992 and was replaced by a new station.

However, as the public's consciousness improves, many proposals have been made to rebuild the old station, but new challenges have arisen.

Shan says that even buildings like the "great 10" are not perfectly safe. Though proposals to include them in a national list of cultural heritage sites have been discussed for years, they have not been approved by authorities for the old reason－they are "too young".

The Overseas Chinese Hotel, which ranked among the top 10 earlier, was demolished in 1988.

When the National Museum of China was being renovated in the 2000s, its facade was planned to be completely changed. The idea was dismissed after a fierce debate.

"More studies of China's 20th-century architectural heritage are needed to avoid such incidents from happening again," Shan says.

"No other century in human history has created such abundant architecture in such diverse styles. More and more heritage sites of that time have been globally recognized."

Since 2000, when UNESCO mentioned the urgency to safeguard 20th-century architectural heritage, many countries made protection of such sites a priority.

Sydney Opera House was listed as a UNESCO World Heritage site in 2007. Seventeen structures worldwide, which were designed by the late French architect Le Corbusier, also got the status in 2016.

Heritage recognition is improving in China.

Ma handed a list to the International Union of Architects in 2004 that included 22 of the most-important Chinese architectural-heritage buildings from the 20th century, promoting an official identification of their status in China.

The nation's first list of key architectural sites of the 20th century was released by the Chinese Society of Cultural Relics and the Architectural Society of China in 2016.