A state of emergency has been declared at a second nuclear power plant in Japan, the International Atomic Energy Agency has said. "Japanese authorities have informed the IAEA that the first, or lowest, state of emergency at the Onagawa nuclear power plant has been reported by Tohoku Electric Power Company," a statement said, according to the AFP news agency. The alert was declared "as a consequence of radioactivity readings exceeding allowed levels in the area surrounding the plant". "Japanese authorities are investigating the source of radiation," it added.