Japan Airlines said on Wednesday a maintenance crew at Narita Airport discovered smoke coming from the main battery of one of its Boeing 787 jets, two hours before the plane was due to fly to Bangkok from Tokyo.

The latest incident involving Boeing's newest jetliner comes a year after overheating batteries on 787s prompted aviation regulators worldwide to ground the aircraft for more than three months.

Maintenance workers found smoke and unidentified liquid coming from the main battery, and alarms in the cockpit indicated faults with the power pack and its charger. The airline said no other equipment was affected by the incident.

The cause was not immediately known, and the airline is investigating the incident.