SHANGHAI (May 17, 2:15 p.m. ET) -- With China’s auto market surpassing the United States as the world’s largest by number of cars sold -- and showing no signs of giving that up -- local plastics-related auto suppliers are boosting investments to handle the expected growth.

They include companies from large, established suppliers like Minth Group Ltd. and battery maker Camel Group Co. Ltd. to newer entrants like Hong Kong-based Eva Precision Industrial Holdings Ltd. Such companies are investing to grow capacity and, in some cases, to intensify efforts in new energy areas like electric vehicles.