legal ground
Article 34 of the Measures for the Administration of Urban Real Estate Mortgage
If the real estate with the legally obtained house ownership certificate is mortgaged, the registration institution shall record his rights in the original house ownership certificate, and the mortgagor shall accept it. And issue the house ownership certificate to the mortgagee. Where a pre-sale commercial house or a project under construction is mortgaged, the registration institution shall record it in the mortgage contract. If the mortgaged real estate is completed during the mortgage period, after the mortgagor obtains the certificate of real estate ownership, the parties concerned shall re-register the real estate mortgage.