(File photo: Chinanews.com)

Unmanned gyms that are open 24 hours a day have been gaining in popularity in Guangzhou, reports Guangzhou Daily.

The gyms are usually much cheaper than traditional gyms, with members paying as little as 10 yuan (around 1.50 U.S. dollars) to exercise for one hour.

Customers can buy a membership by registering online using an app and paying a deposit. They can also often buy premium services through the app, such as booking a session with a personal trainer.

But using an unmanned gym does have some drawbacks, according to experts. Because most of the time there are no staff members on-site, there's no one around to help customers who have questions about the exercise equipment, or in case they injure themselves during their workout. 

And the amount of space and the number of exercise machines is usually relatively limited at unmanned gyms compared to regular full-service gyms.