Sources said the involved center is understood to be a Kowloon Bay outlet of Physical Fitness & Beauty - the second largest fitness chain in the city.

The suspect, Chan, was arrested for obtaining property by deception in Tai Po on Wednesday. He was detained for questioning as of last night and could face up to 10 years in jail if convicted.

Police said the suspect had worked on and off as a fitness coach for the center before he quit in October and subsequently conned the victim.

Sau Mau Ping Criminal Investigation Unit inspector Tam Lok-yan said the suspect carried out 11 scams between October and January, during which the victim was duped into giving him HK$2.6 million in cash and four luxury watches worth over HK$900,000 in total.

Tam said the victim, a retired clerical worker, first joined the center in 2012 due to health concerns and paid HK$2 million in gym membership and coaching fees for 2012 to 2027.

She said the victim then got acquainted with the suspect when he became her personal trainer for a course at the center last year.

"The victim wanted to get her gym membership [and coaching fees] refunded," Tam said.

"On learning about the matter, the suspect told the victim he could help her get her fees refunded, and asked her to give him money and four luxury watches as a 'handling fee' in return."

Tam said the case came to light when the victim made a report to the police on Sunday, saying she could not get her refund..

The police appealed to citizens to pay attention to the terms and conditions of package offers or courses that span over a long period or involve a large sum of money.

"When in doubt, citizens should ask merchandisers about the package offers or courses to avoid falling victim to criminal traps or handing over money and valuables to strangers," police said.

They did not rule out further arrests relevant to the case.

The victim was said to have given the money to the suspect within a month of his resignation.