Japan Transport Safety Board said the battery onboard All Nippon Airways Co Ltd's Boeing 787 flight was blackened and carbonized on the inside, Kyodo News said on Thursday.

The JTSB inspector told reporters at Takamatsu Airport in western Japan, where the ANA flight made an emergency landing on Wednesday, that the battery had leaked oil and was five kg lighter than usual, Kyodo said.

(Reporting by Mari Saito; Editing by Daniel Magnowski)