PG&E power lines caused two small fires in Lafayette and one fire in Martinez on Oct. 27, authorities said.

Power lines caused the two fires in Pleasant Hill Road and Camino Diablo in Lafayette, and investigations are ongoing, according to the Contra Costa County Fire Protection District.

Power lines and a transformer also sparked the 50-acre Forest Way fire in Martinez, according to a completed investigation. The fire briefly forced evacuations of 2,400 people and led to one firefighter injury. No structures were damaged.

PG&E said earlier this week the Lafayette fires started around the same time as two PG&E electrical malfunctions in a filing with the California Public Utilities Commission.

“We are cooperating with the investigations into the recent fires and will continue to respond to requests for documents and other information related to those investigations,” PG&E said.

The 7-acre fire near Camino Diablo destroyed three Lafayette Tennis Club buildings. It also damaged a home and led to the evacuation of 1,100 people.

Power was not shut off in the area because there was low risk of fire, PG&E previously said.

Con Fire is confirming the causes of the Oct. 27 wildfires in Lafayette and Martinez as power lines. See following for details. pic.twitter.com/nzRQp0ebE9 — Con Fire PIO (@ContraCostaFire) November 1, 2019

Roland Li is a San Francisco Chronicle staff writer. Email: roland.li@sfchronicle.com