The attack happened at the front door of the consulate on Laguna Street off Geary Boulevard.
At 9:35 p.m. Wednesday, a security camera mounted on an apartment building across the street from the consulate shows a van stopping at the curb next to the entrance. Moments later, a fire broke out.
A witness says she saw two men outside the consulate. Investigators say they poured two buckets of gasoline onto the front door before setting it on fire.
No one was hurt in the fire that charred a doorway, damaged the lobby and burned upward toward the roof.
Chinese Consulate Press Attache Wang Chuan called the act despicable.
"The arson attack is a violent attack targeted at the Chinese Consulary Institution in the United States, causing severe damage to the consulate facilities," he said.
U.S. State Department spokesperson Marie Harf said it was too early to judge whether security at the consulate had been adequate.
"We take this incident very seriously, and the Bureau of Diplomatic Security is working with the FBI and local authorities to investigate and apprehend the perpetrators," Harf said.
The FBI said it does not believe it was an act of terrorism. FBI spokesperson Peter Lee says the blaze was caused by a gas-based device with accelerants. He adds that no bomb-making materials were found, and there were no traces of an explosion.
"At this point in time our initial assessment is that this appears to be, most likely, a criminal matter as opposed to a national security matter," said David Johnson, FBI Special Agent in Charge SF.
But just in case, San Francisco police assigned a unit to the consul general's residence in the Monterey Park district of the city.
This is the second time the consulate has been targeted by arsonists.
In 2008, a group poured flammable liquid on a metal security gate outside the building. No one claimed responsibility, but investigators believe it may have had something to do with China's crackdown in Tibet.
That fire came on the day San Francisco supervisors heard public comment on China's human rights record months prior to the start of the 2008 Summer Olympics in Beijing. The issue arose because of the scheduled Olympic torch run through San Francisco.
The FBI said the 2008 incident was not related to Wednesday's fire.
On Thursday, the consulate was business as usual. Visa applicants went through another entrance. But they couldn't miss the fire damage. Many had strong opinions about what happened.
"Terrorism, right, it's terror, the nature should be the same as any group attacking the U.S. Embassy Consulates in foreign countries," visa applicant Leo Young said. "And I think the U.S. government should condemn this as a terrorist attack.
A reliable source who has seen a consulate security video says one of the arsonists is a man who appears to be Asian, wearing glasses and jeans.
(The Associated Press contributed to this report)
