I believe that so long as your debt-to-income ratio does not exceed 50% or whatever it is these days (lower for properties exceeding HKD 10 or 12m?), you should be okay.
If you get a pre-approval from the mortgage lender, then take out a personal installment loan, and then apply for the mortgage after drawing down the first loan and putting down the initial deposit, the bank providing the mortgage will be able to see, on your credit report, that you have taken that first loan.
Again, so long as both loans keep you within the maximum debt-to-income ratio, you are okay. If not, then you could be in a bit of trouble.
Of course, it would be wise to check with the mortgage lender first, and run it by them before you even take out your personal installment loan. And let them know how much that loan amount, and your EMI will be and over what period.