It was the first theft in 20 years from the historic site, spokesman Feng Nai'en said, adding that security would be increased.
"For this to happen here shows us that, No. 1, we need to speed up the modernization and installation of our security systems," Feng said. "No. 2, we need to investigate carefully and find out if we can implement better, more modern and more sophisticated security systems."
Guards saw a suspect fleeing the scene early Monday but failed to nab him, Feng said.
An investigation found that nine pieces - all small Western-style gold purses and mirrored compacts covered with jewels made in the 20th century - were missing from the temporary exhibition, on loan from the private Liang Yi Museum in Hong Kong.
Two of the missing items were recovered nearby and were slightly damaged.
Feng said the entire Palace Museum will be checked to see if any other items are missing.
Wang Xiahong, curator of the Liang Yi Museum, refused to reveal the value of the stolen items, which belong to Hong Kong art collector Fung Yiu Fai. She said that despite the theft, the exhibition would continue and other pieces would be added to the show, which is temporarily closed but expected to reopen soon.
The museum's deputy director, Ma Jige, told reporters he felt "very guilty and sorry" about the theft. He stood up and bowed to Wang in a show of remorse.
Karen Smith, a Beijing art curator and historian, said the theft was "a big loss of face" for the museum but would probably result in much improved security at the sprawling landmark.
She also noted that the robbery targeted items of relatively low value and prestige, not the museum's best-known treasures such as its large collection of rare and delicate scroll paintings. Those pieces are undoubtedly much better protected, she said.
"If you were really going to go and steal something from the Palace Museum, there's a lot more valuable things you could make off with," Smith said.
It wasn't immediately clear whether future cooperation with other international exhibitors would be affected by the incident.
Hundreds of thousands of rare and valuable pieces originally housed in the Forbidden City were secreted away to Taipei's Palace Museum when Taiwan split from the mainland during a civil war 62 years ago.
China still claims Taiwan as part of its own territory and insists the art at Taipei's Palace Museum rightfully belongs on the mainland.
Beijing's Palace Museum lent dozens of items to Taiwan for an exhibition in 2009, but Taiwan is still hesitant to lend China artifacts out of fear that they would not be returned.
An official with Taiwan's Palace Museum said the ownership concerns mean there are no immediate plans for an exhibition in China. The official spoke on condition of anonymity because she is not authorized to talk to the media.
---
Associated Press writer Debby Wu in Taipei contributed to this report.
