Authorities in Dianjiang county, Chongqing, continued to monitor the region's air and water quality yesterday, a day after benzene storage tanks exploded at a local pharmaceutical plant. The blasts at the Waycome Pharmaceutical Plant killed one person and injured four others, but did not appear to have contaminated the nearby Long River or affected Chongqing's air quality. More than 6,000 students were forced to evacuate two nearby schools on Thursday and dozens of fish were seen floating in the Shuanghe River, a separate waterway. The Dianjiang environmental authority has banned people using water from the Shuanghe. Classes at one local secondary school have been cancelled until Monday. An official from Xinmin, a township under Dianjiang county's administration, said many students were receiving treatment for unspecified illnesses yesterday. 'The evacuation of the school should have been more efficient,' the official said. 'The benzene in the air has decreased to a safe level and the area's water quality will soon be normal.' The official said the plant had been shut down until it gained the necessary production safety certification. He said the blast was caused by human error and the plant would soon be operational again. Factory sales manager Zou Yang said the explosion was simply an accident and the plant's safety was being inspected by government authorities. 'We have been granted the good manufacturing practice certification by China's State Food and Drug Administration,' Mr Zou said. The factory was opened in 1999 and is one of more than 40 chemical and pharmaceutical plants in the area. The explosion raised safety concerns among nearby residents. 'There are many dangerous chemical factories here. It's like we are living among dozens of live bombs,' resident Zhou Hong said.