(Reuters) - Malaysian state investor Khazanah Nasional Bhd has offered to buy General Electric's $1.8 billion stake in Thailand's Bank of Ayudhya , sources familiar with the matter said, pitting it against Japan's biggest lender Mitsubishi UFJ Financial Group (MUFG) <8306.T>.

The bid by Khazanah was a surprise, the sources said, declining to be identified as the information is not public.

The proposed acquisition would be the largest purchase of an overseas banking asset by Khazanah as the sovereign wealth fund plays catch-up with Singapore state investor Temasek Holdings Pvt Ltd . Khazanah currently manages a portfolio that is just a quarter of the $158 billion of assets held by its neighbouring rival.

Khazanah had in the past shied away from taking large banking stakes overseas, focusing on healthcare assets in Singapore and Turkey as well as real estate deals. A successful bid for GE's stake would mark a shift in Khazanah's strategy and bring it closer to that of Temasek's - which owns large shares in Standard Chartered , China Construction Bank <601939.SS> and Indonesia's Bank Danamon .

The Malaysian state investor is acquiring assets in neighbouring emerging markets with the outlook for Southeast Asian economies resilient in the face of global economic uncertainty.

General Electric Co is selling its remaining 25.3 percent stake in Bank of Ayudhya as it divests non-core assets across the world.

Officials from Khazanah and GE declined to comment.

The Malaysian state investor is also picking up insurance assets.

Khazanah, which owns a nearly 30 percent stake in Malaysia's second-biggest bank CIMB Group Holdings Ltd , recently teamed up with Sun Life Financial Inc to buy a 98 percent stake in an insurance joint venture between CIMB and Aviva .

This week, Khazanah made a preliminary bid to acquire a $500 million stake in unlisted Thai Life Insurance Co Ltd.

(Reporting by Saeed Azhar in SINGAPORE and Taiga Uranaka in TOKYO; Additional reporting by Ngui Yantoultra; Editing by Denny Thomas and Ryan Woo)