Japanese pharmaceutical giant Eisai says some of its group's servers have been hit by a ransomware attack. The company is checking to see if any data was leaked.

Eisai detected the incident late on Saturday night. It says internal systems for logistics and other functions have been taken offline both in and outside of Japan. Corporate websites and email systems continue to operate normally.

The company has set up a taskforce to investigate. It says it's working closely with outside experts and the police to ensure its systems are secure and it can make a full recovery.