As the museum expected, not all of the 2,000 who had made reservations turned up the previous evening. Among those who did were Wang Junhan, 9, his mother and some of his classmates at the Shanghai Fushan Zhengda Foreign Language Primary School.

"During the day there's always a long line of people at the gate, and in the evening it's less crowded and quieter, so that's a much better time to come," said Junhan's mother, who did not want to be identified.

"I've been with my son to the Louvre in Paris and the British Museum in London," said the mother, who works in the finance industry.

"The exhibitions one sees in China's museums are just as good as anything you see anywhere else, but it would be great if they had games for children so they could have a bit of fun, whether with adventures or puzzle games."

Huang Hui, a security officer in the exhibition hall, said those who visit the exhibitions in the evening tend to be quieter and spend more time appreciating the exhibits.

Among the visitors on the evening of Aug 9 were Wang Xuan of Shanghai, in her 20s, and a friend. They had opted to visit the museum that rainy evening because "during the day in summer it's just too hot," Wang Xuan said.

She felt happy and refreshed, she said, a bonus being that "we don't have to go to work tomorrow."

For all the balm that a relaxing night visit may deliver to visitors, extended hours also obviously place more pressure on museum staff, among them those who take care of maintenance and security.

The Memorial for the Site of the First National Congress of the Communist Party of China in the Xintiandi district of Shanghai, opened as a trial on the evenings of July 1 and 5, receiving an average of 5,000 visitors each day, and "it is a new challenge to ensure the safety of the memorial and cultural relics", a museum official said.

Opening in the evening requires more staff and other resources, said Qiu Zhengping, deputy director of the Shanghai History Museum, one of the 14 museums to extend into night hours every Friday since July.

"Each department needs to have someone staying on for the evening, involving security and property management staff."

In addition, some exhibition items are ill-suited to long exposure to the light, and some new media interactive devices were designed to operate eight hours a day.