At least 21 people died and 11 others were injured on Friday in a collision involving four vehicles on a highway in China's Hunan province, local authorities said.The accident occurred around 9.50 a.m. (local time) on Hunan section of the highway linking Shanghai and Kunming, capital of Yunnan Province, Xinhua news agency quoted an official of Hunan as saying.A truck crashed through a guardrail and hit a coach, which caught fire later. The accident also caused two other vehicles to collide on the highway, the official said.The driver and a passenger in the truck were under police custody for further investigation. The injured have been sent to hospitals.