Supermarket operator OK Corp, which owns 7.69% of Kansai Super Market, also said in a statement that it would oppose the plan at Kansai's extraordinary shareholders meeting on Oct. 29, adding that it had first approached Kansai Super in June.

Kansai Super, meanwhile, said in its statement that there was no change to its plan with H20 Retailing, which had been carefully weighed against OK Corp's proposal.

The deal with H2O Retailing, which is the chain's top shareholder with a 10.66% stake, was announced at the end of August but does not sufficiently explain how minority shareholders' rights will be protected, OK Corp said.

The counterbid sets up an unusual Japanese corporate face-off as supermarket operators grapple with a shrinking and aging customer base.

Shares of Kansai Super closed at 1,374 yen on Thursday and did not trade on Friday with a glut of buy orders and after being suspended for most of the day.

A spokesperson for H2O Retailing said it had the stronger bid but it was for Kansai Super shareholders to decide how to vote.

($1=110.0200 yen)

(Reporting by Chang-Ran Kim and Sam Nussey; Editing by Christopher Cushing, Stephen Coates and Uttaresh.V)