Eleven people were on Tuesday convicted of rioting outside the government headquarters three years ago.

The District Court heard that about 500 protesters assembled outside the complex in Admiralty and hurled petrol bombs at and vandalised the premises on September 29, 2019.

Lawyers from the defence had disputed the size of the area where the riot occurred and argued that there was no direct evidence showing their clients caused a breach of the peace, while two of the defendants had claimed they were there looking for their missing friends.

In handing down his ruling, judge Frankie Yiu said all prosecution witnesses were truthful in their account of what happened that day, whereas the evidence by the two defendants claiming they were there looking for their friends was untrustworthy.

He said despite repeated warnings by the police, the protesters didn't disperse and continued their attack on the government headquarters.

The judge said although the defendants were arrested in different locations nearby, they were not innocent bystanders and knew they were part of the same group, especially when the riot had taken place for some time.

Sentencing has been adjourned to September 9.