China National Offshore Oil Corp's (CNOOC) chairman Song Enlai told reporters in Beijing yesterday that the state-controlled company was already pumping oil from Chunxiao gas field, known as Shirakaba in Japan, Reuters reports.

Japanese Chief Cabinet Secretary Yukio Edano said Tokyo was looking into the matter after the Asahi newspaper in Japan reported Song's comments this morning.

"It is very regrettable that a media report naming a CNOOC official has been released. We are checking with the Chinese side about this," Edano told a news conference.