Sumitomo Life Insurance Co. is among companies preparing to bid for a stake in the life insurance unit of PT Bank Negara Indonesia, according to two sources.

Sumitomo Life, Japan's third-largest life insurer, is weighing an offer for a 40 percent stake that may be valued at as much as $800 million, the sources said, asking not to be identified because the deliberations are private. The Osaka-based company has dropped out of bidding for part of Thai Life Insurance, leaving Meiji Yasuda Life Insurance Co. as the sole remaining suitor, two sources said.

Bank Negara, controlled by Indonesia's government, plans to start the sale of the insurance unit stake in the next two weeks, the sources said. The deal follows the sale of a minority holding in the life insurance unit of PT Panin Financial Tbk to Dai-ichi Life Insurance Co. for 3.3 trillion rupiah (about ¥32.4 billion) this month.

Buyers, attracted by an emerging middle class getting coverage for the first time, have spent more than $6.6 billion acquiring insurance assets in Southeast Asia over the past two years, data compiled by Bloomberg show.

Both Sumitomo Life and Meiji Yasuda made final offers for a 15 percent stake in closely held Thai Life, Thailand's second-largest life insurer, sources said last month. The bids valued the stake at as much as $700 million.

Kousuke Miyatake, a spokesman at Sumitomo Life, declined comment, as did officials at Meiji Yasuda and Thai Life. Yap Tjay Soen, finance director at Bank Negara, couldn't immediately be reached. Reuters earlier reported that Meiji Yasuda had entered exclusive talks for a stake in Thai Life.