The crash was reported at 4:07 p.m. at the intersection of Market and Fifth streets, fire spokeswoman Mindy Talmadge said.
Two people were transported to the hospital with minor injuries, Talmadge said.
She did not immediately have more details on the nature of the incident.
San Francisco Municipal Railway officials were not immediately available for comment, but the agency's Twitter feed said the F-Market & Wharves line was being affected by the downed wires as of 5 p.m.
ABC7 News contributed to this report.