San Francisco police said Thursday they will patrol China's consulate around the clock after Chinese officials called for better protection of its diplomats following an apparent arson attack New Year's Day.

The FBI is leading the investigation into the attack, which occurred about 9:30 p.m. Wednesday when an unidentified person emerged from a mini-van with two gas canisters, emptied them on the consulate's front doors in downtown San Francisco and ignited them.

San Francisco firefighters, police and U.S. State Department officials extinguished the flames within minutes, but didn't find the arsonist. The fire caused severe damage to the building's exterior, the Chinese Consulate said in a statement. Photos showed the building's facade charred black from flames and smoke. There have been no arrests.

Chinese officials called the incident a despicable attack and urged the U.S. government to solve the case "as soon as possible" and enhance protection for all Chinese diplomatic missions and staff in the country.

U.S. officials are taking the incident very seriously, State Department officials said in a statement. The State Department's Bureau of Diplomatic Security detail is working with the FBI and San Francisco authorities to find the arsonist.

The attack appears to be an isolated incident, FBI spokesman Peter Lee said. The consulate has requested 24-hour patrols by San Francisco police until further notice, department officials said Wednesday. The department similarly increased its presence around the consulate after an incendiary device was thrown at the building in 2008, police officials said.

State Department officials said there did not appear to be any threats against the consulate leading up Wednesday's incident.

joseph.serna@latimes.com