Smoke and fire billow from a chemical plant after an explosion in Lanzhou, capital of northwest China's Gansu province，January 7, 2010. The blast that happened at around 5:30 p.m. on Thursday left five people missing and five injured, including one in critical condition, Xinhua reported.  [Photo/Xinhua]

Fire engines arrive at a chemical plant after an explosion in Lanzhou, capital of northwest China's Gansu province，January 7, 2010. The blast that happened at around 5:30 p.m. Thursday left five people missing and five injured, including one in critical condition, Xinhua reported.[Photo/Xinhua]