None of the employees were injured, but some of the furniture in the office burned down. According to Japanese media, the fire broke out on the third floor of the Nintendo headquarters at 13:00 local time. Eight fire trucks responded to the call, but the employees were able to extinguish everything before their arrival.
It is not yet known for sure what caused the fire. But it is assumed that the cause could be a faulty device that was charging at that moment.
Note that in early July, Nintendo developed an action plan in case of emergencies that could affect its headquarters.