China's declaration is inutile based on UNCLOS article 298.....
SECTION 3. LIMITATIONS AND EXCEPTIONS
TO APPLICABILITY OF SECTION 2
Optional exceptions to applicability of section 2
1. When signing, ratifying or acceding to this Convention or at any time thereafter, a State may, without prejudice to the obligations arising under section 1, declare in writing that it does not accept any one or more of the procedures provided for in section 2 with respect to one or more of the following categories of disputes:
5.declaration, or the withdrawal of a declaration, does not in any way affect proceedings pending before a court or tribunal in accordance with this article, unless the parties otherwise agree.