The US embassy complex is in Beijing's Chaoyang District.

Witnesses have posted images on Twitter of smoke surrounding the building. Another bystander said there had been injuries, the Herald Sun reported.

The explosion occurred around 1 p.m. in an area where many Chinese citizens line up each day to apply for visas, The New York Times reported.

According to Chinese media reports, a witness said police took away a woman spraying petrol on herself in a suspected attempt at self-immolation.

Photos and videos emerging online of the explosion on Chinese social media site Weibo showed smoke billowing from the area with police creating a roadblock around a vehicle, Hong Kong Free Press said.