The accidents occurred on an expressway in Henan province that links northeast and south China and were blamed on low visibility caused by the heavy fog.
One of the accidents involved more than 10 vehicles, state-run Xinhua news agency reported.
Three people died on the spot, while another three died after being taken to hospital. All of the injured have been sent to two nearby hospitals. Their condition is not yet known. An investigation into the accidents was under way.