Philippines' San Miguel Corp (SMC) said it was keen to gain a majority in Manila Electric Co by buying a 13.4 percent stake of the Lopez family in a deal that could be worth as much as $840 million.

Only if invited by Lopez to bid, yes SMC will bid, Ramon Ang, San Miguel's president, told Reuters in a text message.

Ang said San Miguel would partner with a Japanese group, which he did not name, to bid for the Lopez group's stake in the country's biggest power distributor.

The Lopez family was not available for comment.

Meralco has become an attractive target for both food-to-power conglomerate San Miguel and Philippine Long Distance Telephony Co. as both firms can piggyback on its retail electricity network to offer telecommunications services.

The PLDT group said in May it controls about 48 percent of the power utility, together with some business partners and the remaining stake held by the Lopez family through its power conglomerate First Philippine Holdings Corp.

PLDT said on Monday it had first rights on the 13.4 percent stake held by the Lopez family but declined further comment.

San Miguel currently has a direct 27 percent stake in Meralco which it bought for over $600 million last year. It has said it controls a total of about 43 percent in Meralco through holdings of its business allies.

Meralco said it had a total of 1.1 billion outstanding shares. San Miguel's 13.4 percent stake purchase in Meralco could be worth as much as about 40 billion pesos ($840 million) based on Monday's highest price of 270 pesos per share in Meralco.

Shares of Manila Electric jumped as much as 10.6 percent in early trade. San Miguel's B shares open to all investors slid 0.76 percent and its A shares exclusive to locals were flat. PLDT gained 1.43 percent.

($1 = 47.7 pesos)

(Reporting by Rosemarie Francisco; Editing by Anshuman Daga)