While some automakers are enjoying double-digit growth in China, Japanese auto firms are struggling, The Wall Street Journal reported. Toyota (TM.NYSE, 7203.TYO) said sales declined 6.5% last month from a year ago, while Mazda’s (7261.TYO) reported sales fell 15% in April and 25% in March. In contrast, General Motors (GM.NYSE) said sales rose by 15% last month. Analysts say that a number of factors are hurting Japanese auto sales in China. Tensions over islands claimed by the two countries hurt Japanese auto sales in the second half of 2012, and companies are still feeling those effects. However, increased competition in the sector has also taken a toll on sales. Some Japanese car makers say they will try to boost consumer confidence by offering insurance if cars are damaged in future anti-Japanese riots.