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A 26-year-old man detonated an explosive on the street outside the US Embassy in Beijing Thursday, police said, injuring himself before he was taken away by authorities.

The explosion, which could be heard several blocks away, took place outside the southeast corner of the compound at about 1 p.m. local time (1 a.m. ET), sending a large plume of white smoke into the air above the embassy.

“There was one individual who detonated a bomb. Other than the bomber, there were no injuries and there was no damage to embassy property. The local police responded,” a US Embassy spokesperson said in a statement.

An area outside the embassy, in the capital’s Chaoyang district, was immediately cordoned off by authorities following the incident. By the time reporters arrived at the scene, only a small amount of debris could still be seen.

One IT worker who was less than 40 meters from the scene when the incident occurred told CNN he saw police were running towards the explosion.

“There was a lot of smoke and it smelled a lot like fireworks and matches,” he said.

Another woman said she heard a bang before the whole area filled with smoke. “Everything over there was smoke,” she told CNN pointing at the road outside the embassy.

Police in Beijing said they were investigating the explosion on Thursday, adding the bomber had only injured his hand and his condition was non-life threatening.

“He is hospitalized and no one else was injured. His surname is Jiang, 26, from Inner Mongolia. Case is under further investigation,” the statement said. There is no information at this stage on what Jiang’s motivation might have been.

There are conflicting reports on the nature of the explosive, with the US Embassy spokesperson describing it as a “bomb” and the Beijing police saying it was a “firecracker.” There was no mention of the US Embassy in the police statement.

After the initial reports, news of the incident was very quickly censored on Chinese social media. Within hours almost all mention of the explosion had been wiped clean from WeChat and Weibo, leaving only the official police statements.

Security incidents are highly unusual in the tightly-policed Chinese capital. Speaking during his daily press conference, Foreign Ministry Spokesman Geng Shuang said the explosion was an “isolated security incident.”

“Chinese police have dealt with it in a timely and proper manner,” he told journalists.

The US Embassy in Beijing, which opened in 2008, is one of the most secure in the world, with state of the art technology and a heavy security presence.