(LEAD) Bus carrying about 20 S. Koreans plunges off bridge in northeastern China

(ATTN: UPDATES throughout with details; AMENDS dateline) JIAN, China/SEOUL, July 1 (Yonhap) -- A bus carrying about 20 South Korean officials on Wednesday plunged off a bridge in the Chinese city of Jian, northeastern province of Jilin, a South Korea