The head of a union that represents gym workers warned customers of the shuttered Physical Fitness chain on Saturday that a new operator which took over one of its sites does not appear on the official register.

The Wan Chai location reopened under the name "Healthy" this week, with Physical members invited to use it if they signed a consent form.

Rex Wong, who chairs the Hong Kong Fitness Professionals Association, told RTHK that "Healthy" could not be found in the Companies Registry (CR).

"This is a new company. We didn't know they were registering from the CR. I was scared how to provide the service with the customer, and then the person who provided the trainer, because maybe we got some adjustment from Physical," he said.

"We are not guaranteed everything for customers."

Wong urged the government to enhance regulation over pre-payment arrangements in the fitness and beauty sectors to better ensure consumer rights. Many Physical customers reported signing multi-year contracts.

On Friday, the Consumer Council suggested customers may want to wait before signing the consent form, as the terms and conditions were "unclear".

"The name of the company operating Healthy [is missing]. Hence consumers are unable to ascertain the background information, qualifications and status of the operator," it said, adding that the form stated that Healthy has "no obligation" to provide users the services owed by Physical.

Physical abruptly shut down its 14 branches, but insisted the closure was "temporary" as talks with a new investor were ongoing. As of 6pm Friday, the council had received 3,666 complaints related to unfulfilled contracts, involving more than HK$123 million.