Chinese police have released few details about the ramming, spokesman Richard Buangan said. The embassy did not report the incident at the time; Buangan was responding to queries from The Associated Press, which learned of the incident on Friday.
The three men were immediately taken into police custody and the embassy's security officers were seeking more information, Buangan said. Their identities are unknown to the embassy, he said.
In a brief statement faxed to the AP, China's Foreign Ministry confirmed the incident and said the driver appeared to be mentally ill.
"On Jan. 28, a male of Chinese nationality smashed a car into the south gate of the U.S. Embassy in China, causing damage to the car and the gate but no injuries or deaths," the statement said.
"After investigation, this man was found to have a mental disorder," it said, adding the case remained under investigation.
The ministry provided no information about the two other men in the car.
Beijing police did not immediately respond to questions about the incident, which they requested by fax.
The incident occurred at around 3 p.m. on Jan. 28, during China's weeklong Lunar New Year holiday. Buangan said the car involved was a Volkswagen Passat and the gate, which was a staff entrance to the complex, was bent inward and cannot now be opened.
Workers on Friday were repairing the gate with drills and welding torches.
Diplomats moved into the new U.S. Embassy in Beijing just last year. The massive complex is the second largest U.S. Embassy in the world after the one in Baghdad and sprawls over an entire city block on Beijing's eastern Chaoyang district.
China has blamed al-Qaida-linked terror cells for attacks in the country's far west, but the capital has been largely peaceful and sentiment among Chinese toward the U.S. has been largely neutral in recent years.