BEIJING, Dec 8 (Reuters) - SAIC Mobility, a unit of top Chinese automaker SAIC Motor (600104.SS) and autonomous driving startup Momenta have begun offering autonomous robotaxis test rides to the public in a Shanghai district as part of a trial, Momenta said on Wednesday. The two firms are testing 20 robotaxi vehicles in Shanghai"s Jiading district to further gauge their viability for commercial use in a trial that will expand to a second Chinese city next year, said Momenta, whose technology is used by SAIC Mobility. SAIC Mobility, a SAIC Motor unit dedicated to robotaxi services, was not immediately available for a comment. Beijing-based Momenta said the two companies are exploring the application of fully autonomous so-called "Level 4" driving technology in urban travel scenarios through the trial. Riders can summon a robotaxi through the SAIC Mobility App with one click, the statement said. Momenta and SAIC Mobility plan to boost the test fleet in Jiading next year by adding 20 vehicles and to expand trial rides to the neighbouring Chinese city of Suzhou with an additional 20 vehicles. Automakers and technology firms are investing billions of dollars in autonomous driving, aiming to take an early lead in what many consider the future of mobility. Last month, Chinese tech group Baidu Inc and self-driving startup Pony.ai won approval to launch paid driverless robotaxi services in China"s capital Beijing. read more