ANTIOCH -- A grass fire on Lone Tree Way damaged a doctor's office and one other building Friday afternoon, but no one was injured, authorities said.

Seven units from the Contra Costa Fire District controlled the 4:15 p.m. blaze in about 25 minutes, fire spokesman George Laing said.

The exteriors of a doctor's office at 3725 Lone Tree Way and of a neighboring building at 3737 Lone Tree Way were damaged, Laing said.

"The vegetation fire caused embers, which then spread to the adjacent buildings through the roofs," Laing said.

Investigators were still determining what caused the fire, Laing said. Financial estimates of the damage to the buildings were unavailable.

Rick Hurd covers public safety. Contact him at 925-945-4780 and follow him at Twitter.com/3rdERH.