To check the business registration number in Hong Kong, you can visit the Companies Registry’s Free Search Services Cyber Search Centre (CSC) website at https://www.icris.cr.gov.hk/csci/ to conduct company searches (24×7) on the current data of registered companies and image records of documents registered and kept by the Registrar of Companies (the Registrar). You may log in the CSC as an Unregistered Online User. If you conduct company searches frequently, you may register as a Registered Online User. This system allows individuals and companies to conduct various company registration and search activities online, such as filing annual returns, registering for business licenses, and searching for company information which includes the business registration number.
Another option is to request the information from the business itself. Businesses in Hong Kong are required by law to display their business registration number on their official documents, including invoices, receipts, and letterheads. So, if you have any of these documents from the business, you can check the number there.