City of Mercer Island issued the following announcement.
Today at approximately 1:50pm, Mercer Island Fire Department units were dispatched to the 2400 block of 70th Avenue SE for reports of "smoke in a residence." Upon arrival, crews witnessed heavy, pressurized smoke exiting the attic and upgraded the response to a structure fire. This brought a total response of two Battalion Chiefs, four engines, two ladder trucks, and medical aid units. The Mercer Island Police Department assisted with traffic control and PSE turned off utilities to the structure.
There was significant damage to the structure and its contents, but no injuries to civilians or firefighters; the house was unoccupied at the time. MIFD received assistance from the Bellevue Fire Department, and Eastside Fire and Rescue under mutual aid agreements. The cause of the fire is still under investigation.
Original source can be found here.