Nearby, in the shadows of the People's Meeting Hall, about 80 people were lined up for a beginners' class in the tango, while more than 200 others glided gracefully across an empty concrete parking area. The romance was blighted only by the traffic on a flyover.
Ask a Zhengzhou resident what to do of an evening, and they are likely to suggest a spot of outdoor dancing. Many Chinese cities have dancing in the parks, but Zhengzhou seems to have it on every street corner. From a 17-year-old female medical student to a 71-year-old retired man, they roll up outside the museum. Every night.
Nearly 4,000 years ago, this region was the cradle of Chinese civilisation at the start of the Shang dynasty. These days, Zhengzhou is best known as a sprawling inland industrial transport hub. Its ailing state industries have shed hundreds of thousands of employees who now vie for work with waves of migrant workers.
Like all Chinese cities, Zhengzhou also has its new rich, catered for by expensive seafood restaurants and fancy karaoke clubs. But it is the night-time dancing which is within everyone's reach - at just 1 yuan (8 pence) entrance fee or around 6 yuan (50p) for a monthly ticket.
No one is quite sure why Zhengzhou is gripped by this craze, which residents say has grown in popularity since the late 1980s. But for many people it is now a daily fixture in their lives.
"She's the most skilful," said 42-year-old Gao Xiuying, a scientific researcher, pointing at a middle-aged woman in a red sweater. "If she does not come, the synchronised dancing is disorganised. She usually comes every night."
Chai Mengyue, whose given name translates as Dream of the Moon, did indeed have a level of co-ordination that most of the others lacked. The 51-year- old retired textile worker had thus been cast in the role of unpaid "dance teacher by obligation", said Mr Gao.
"I'm an amateur teacher," said Ms Chai. "I had to take early retirement at 48. Before that I did not have time for dancing."
Just three years ago, one quarter of Zhengzhou's workforce was in the loss-making textile industry, a sector which throughout China is currently slashing its workforce. In her new life, Ms Chai is mistress of the dance on the west side of the square, where those who favour the individual synchronised dancing followed her repeated routines - again, and again and again. "It's popular as a spare-time hobby and for exercise," she said.
On a busy night, the museum venue attracted 700 people, said the ticket- seller. She was employed by the museum's trade union branch. The museum work unit still owned the building and was putting it to use as profitably as it could.
So why was dancing so popular in Zhengzhou? "People want to make a more colourful life, especially older women," she said.
But it was the men of Zhengzhou who were the most anxious to improve their dancing skills, it turned out. At the official dancing school run by Qi Duozhen, the "senior dance coach", the number of men noticeably outnumbered women, and women were being offered a 50 per cent discount to enroll.
"Since people's living conditions are improved, they would like to improve their spiritual lives," said Ms Qi, as another teacher, in heels and a sequined red skirt, brought tango to the masses.