SHENZHEN, China, Dec 19 (Reuters) - Four people were killed and another eight injured on Saturday when part of a bridge ramp collapsed in Ezhou City, in China"s central Hubei province, the official Xinhua news agency reported. The bridge collapsed over an expressway, causing three trucks to fall while a car was crushed underneath, Xinhua reported, adding an investigation is under way. Work was being carried out on the bridge when the incident occurred, the report said.