This was reported by local law enforcement on Twitter.

“Radical protesters threw Molotov cocktails into the building of the government complex, creating a serious threat to the security of everyone, including the police on the spot,” the statement said.

Radical protestors threw petrol bombs at Central Government Complex, posing a serious threat to the safety of everyone, including police officers on site.

- Hong Kong Police Force (@hkpoliceforce) September 28, 2019

In late August, the PRC government strongly protested the White House and some US congressmen for supporting detainees in Hong Kong. The Chancellery of the Ministry of Foreign Affairs of China in Hong Kong also accused the US of “criminal activity” in the territory of the Chinese region.