Photos and video clips posted online show smoke, a cordon and a road partially blocked by police as eyewitnesses gather outside a gated compound.
Men in military uniforms were standing guard at the cordon, and many of the eyewitnesses were snapping photos or recording video with their mobile phones.
One video taken in the aftermath shows security personnel, including military and police, working around something under a blue tarpaulin within a cordon.
One person in normal clothes is kneeling next to the tarpaulin.
Chinese and American officials have not yet commented on the incident.
The alleged blast happened in a district where there are a number of foreign embassies, including those of the US, and South Korea.
Other reports from Beijing say Chinese police took away a woman who sprayed herself with gasoline in what was suspected to be a self-immolation attempt outside the US Embassy amid reports of an explosion. According to this report, there was no explosion, but a woman tried to set fire to herself outside of the US embassy in Beijing.
