In a quest to reduce their reliance on one of the world's least profitable banking markets, Japanese lenders are setting their sights on a much more lucrative one: Mexico.

Mitsubishi UFJ Financial Group Inc. and Mizuho Financial Group Inc. are among so-called megabanks expanding in Mexico, riding the coattails of Japanese automakers that are building factories there to serve the U.S. market.

MUFG, as Japan's biggest bank is known, plans to open an office in March in the central Mexican city of Leon to service the nearby factories of automakers including Nissan Motor Co. and Honda Motor Co. Mizuho is seeking to increase the number of employees in the country fivefold as it opens its first banking subsidiary there as soon as September.