No one was hurt in the fire Wednesday night fire that charred the building's doorway, damaged the lobby and burned upward toward the roof.
FBI spokesman Peter Lee said the blaze was caused by an "incendiary device," but didn't specify what it was. No bomb-making materials were found, and there were no traces of an explosion, he said.
Surveillance footage showed a person coming out of a van parked outside the compound with two buckets, pouring the contents on the front of the consulate building and setting it on fire, Wang Chuan, spokesman for the Chinese consulate in San Francisco. The building has a surveillance camera at the entrance of its building located in San Francisco's Western Addition district.
Police and firefighters arrived at the scene around 9:30 p.m. Wednesday as crews brought the flames under control within minutes, fire department spokeswoman Mindy Talmadge said.
A consulate statement called the incident "a sabotage of a vile nature" and said China had urged U.S. authorities to launch an immediate investigation.
The fire caused "serious damage to the facilities of the consulate and endangered the safety of the consulate officials and the citizens living nearby. We express strong condemnation," the consulate statement said.
Lee said he did not know whether the consulate had received any threats recently or any demonstrations at the site.
The FBI is leading the investigation with the help of the Department of State Diplomatic Security Service and the San Francisco police and fire departments.
"The FBI takes any criminal offense directed toward a diplomatic establishment very seriously," Lee said.