The police are not very reliable in Mainland China, and Chinese people are not always eager to call the police even when they have been the victims of a crime.
My understanding is that the police are not terribly effective, but I don't believe that people are generally afraid to call the police.
This might sound odd, but I always looked forward to registering with my local police in China. They always seemed so friendly. But yes, friendliness and effectiveness might not always go hand-in-hand...
Police are notoriously ineffective in the US