The Forbidden City said it would install additional surveillance cameras and upgrade glass windows in the ancient buildings following an incident Saturday in which an antique clock was damaged after a visitor smashed a window of one of the many pavilions.

"We started to replace the windows with unbreakable glass in 2012 and two pavilions of the palace have already been completed. This incident reminds the Forbidden City to accelerate its work of replacing the existing windows," said Zhang Ying, media officer of the Forbidden City.

A man surnamed Wang, 22, from Huanggang, Hubei Province smashed a window of Yikungong, a pavilion of the ancient Forbidden City where imperial concubines lived, the Forbidden City said.

Police arrested Wang, who is being held in criminal detention and is being investigated for deliberately damaging cultural relics, according to the official Sina Weibo of the Beijing Municipal Public Security Bureau Sunday.

Zhang told the Global Times the man's motive is not known.

An ancient clock inside the pavilion was partially damaged. The window has been repaired and the exhibition area was reopened Sunday morning, the Forbidden City said in a press release.

Zhang said the Forbidden City already uses several thousand video cameras to monitor the sprawling museum located in the heart of Beijing. Additional cameras will be installed and more security staff will be added to ensure full coverage of the former emperor's palace that covers 72 hectares.

"The first cameras were installed many years ago so we need to upgrade them to high definition cameras. There are some blind spots in the palace and we need to install new cameras so we can monitor those areas," Zhang said.

Footage from the camera nearest the pavilion window that was smashed shows a man walking up to the building and then walking away with blood on his clothing. His act of vandalism was not captured on video.

It was not the first time that the Forbidden City was involved in a breach of security.

A man, who broke into the Forbidden City in May 2011, stole nine art works made of gold and jewels - all on loan from Hong Kong and insured for 410,000 yuan ($65,000). He was caught and sentenced to 13 years in jail. The incident sparked public concern over security lapses in the Forbidden City, according to a report by the Xinhua News Agency in March 2012.

Liu Zheng, a member of the China Cultural Relics Association, said that the incident on Saturday differs from the previous premeditated robberies, which exposed serious lapses in security. This weekend's incident still shows, said Liu, that the Forbidden City needs to increase security staff.

"The number of visitors increases during the summer and there should be more staff to maintain order and avoid similar acts from happening," he told the Global Times.