An arsonist severely damaged the front door of China's consulate in San Francisco in a "despicable" attack, Chinese officials said Thursday, urging US authorities to protect diplomatic personnel.

The State Department responded by saying it was "deeply concerned" by the reports, and pledged to find who carried out the New Year's Day attack and bring them to justice.

"January 1, 2014, at 9:25 pm, a person from a mini-van parking in front of the main entrance of the Chinese Consulate-General .. poured two buckets of gasoline onto the front door .. and then set it on fire," leaving it "severely damaged," said a statement on the consulate's website.

San Francisco's police and fire authorities, as well as the US State Department's diplomatic security, responded "immediately" it said.

The consulate was closed at the time although a handful of employees were working at the time, according to the San Francisco Chronicle.

But the Chinese statement condemned the "despicable act" which poses "a threat to the safety of the consulate staff and the residents living nearby."

"We urge the US side to take all necessary measures to provide adequate protection for Chinese consular personnel and properties, and bring the culprit(s) to justice as soon as possible," it said.

Police confirmed to AFP they are investigating the incident.

In Washington, State Department spokeswoman Marie Harf pledged to find those responsible.

"The United States is deeply concerned by reports that the Chinese Consulate in San Francisco was damaged after being targeted by an arsonist," she said in a statement.

"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.

"Department officials are communicating with Chinese officials to provide support and updates on the case."

The consulate was the target of a similar arson attack in March 2008, the San Francisco Chronicle reported, saying a group of people poured flammable liquid on a gate behind the building, setting it ablaze.

That incident came as San Francisco authorities were hearing public comment on China's human rights record ahead of the the 2008 Summer Olympics in Beijing, the newspaper said.