Using the software package Sigma developed by Schneider, we automatically discover and prove some combinatorial identities involving harmonic numbers, from which we deduce some supercongruences on partial sums of hypergeometric series. These results confirm some conjectural generalizations of van Hamme's (B.2) and (C.2) supercongruences in some special cases, and extend van Hamme's (A.2) and (H.2) supercongruences to the cases modulo p^4.