An area outside the embassy in the Chinese capital's Chaoyang district is still cordoned off by authorities.
Police have not yet commented on the incident.
Another witness said seven or eight police vehicles were at the scene and the road next to the large complex has been closed off.
A woman has reportedly detained after spraying gasoline on herself outside the US Embassy in Beijing.
The individual was the only one injured in the incident and their condition was not immediately known, the spokesperson added.
Another witness saw Chinese police examining a vehicle outside the building.
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According to the United States embassy spokesperson, the only person injured was the individual who detonated the explosive device.
Another person said a woman was taken away by police after spraying gasoline on herself outside the US Embassy at around 11 a.m., according to The Global Times.
It has not been confirmed whether this was related to the reported explosion.
Witnesses had earlier said they heard an explosion near the embassy and felt tremors.
Developing story, more to come. Check back for updates.