Shenyang is an important industrial center in China and is the core city of the Shenyang Economic Zone, a New Special Reform Zone. It has been focused on heavy industry, particularly aerospace, machine tools, heavy equipment and defence, and recently on software, automotive and electronics.[77] The heavy industry started in the 1920s and was well developed before the second world war.[78][79] During the first five-year plan (1951–1956) many factories were built in Tiexi district.[80] At its peak in the 1970s, Shenyang was one of the top three industrial centers in China alongside Shanghai and Tianjin, and was at one time being considered for upgrading to a direct-controlled municipality.