A husband and wife have been arrested on suspicion of fraud in connection with the supply of bottled water to government offices, police said on Monday.

A 61-year-old director of a trading company and his shareholder wife, 57, were arrested on Sunday at the firm's office in North Point and a flat in Sai Wan Ho.

Their company was believed to have been supplying water to government premises on Hong Kong Island and some outlying islands until officials terminated the contract citing concerns about the firm's operations.

Police said they believe the couple wrongly claimed to have an agreement in place to source water from a mainland supplier which has denied having business dealings with them.

The force said the mainland company only recalls being asked by the firm for water quality reports.

"Our initial belief is that the information was collected to send to the Government Logistics Department, which might lead the latter to believe the quality of the water supplied reached a reasonable level," said Wong Chun-yue, a police chief superintendent.

"This is our initial understanding, and it's also an important direction of our investigation."

Police said they have found around 26,000 bottles of water at a Yuen Long warehouse thought to be from the same batch as those sent to government offices.

Officers said they believe the water came from a plant in Zhangmutou in Dongguan and they will visit the site with the help of mainland counterparts as part of their investigation.

Police also said they are searching for a mainland man in connection with the case, but they are not able to disclose details about him for operational reasons.