Chinese police said there were no other injuries in the incident, which took place near where visa applicants typically line up to enter the embassy for interviews.
The explosion was set off by a man from China’s Inner Mongolia region surnamed Jiang, police said, adding that his injuries were not life-threatening.
Video clips that circulated on social media shortly after the explosion showed smoke in the air outside the embassy compound, and AFP journalists arriving at the scene found heavy Chinese security.
“We heard a rather strong explosion around 1:00 pm (0500 GMT) so we went out on the street to have a look, but very soon the police had cordoned off the area,” said a witness who declined to be identified.
Further details about the incident were not immediately available, with police quickly cordoning off the spot where the blast took place and China’s state-censorship apparatus moving swiftly to block searches for “US Embassy” on the popular Twitter-like Weibo platform.
China regularly sees cases of disgruntled individuals lashing out at society over various grievances or perceived injustices, often harming themselves or others.
AFP journalists said the visa office adjacent to where the blast took place appeared to have resumed operation not long after the incident.
The area where the incident took place is on the outskirts of Beijing and home to several embassies, including those of the United States, India and Israel.