There are two basic types of mortgages you can take out in Hong Kong: General Mortgage and Deposit-Linked Mortgage.
A general mortgage is a straightforward secured loan wherein the bank covers up to 90% of the cost of the property you're buying, which you repay within an agreed period with annual interest. A deposit-linked mortgage is linked to a deposit account that offers a preferential interest rate equivalent to the mortgage's interest, or with one that your deposits can use to reduce your interest in each repayment period.