A High Court jury on Thursday convicted one person and cleared six others over a plot to bomb and shoot police officers in 2019, after Hong Kong's first-ever trial involving United Nations anti-terrorism legislation.

Lai Chun-pong, who was 29 when he was arrested, was found guilty of conspiracy to cause explosion likely to endanger life or property.

He is expected to appear in court next Monday to offer a mitigation plea.

Six co-defendants, Cheung Chun-fu, Cheung Ming-yu, Yim Man-him, Christian Lee, Justin Hui and Lau Pui-ying were cleared of related charges, including conspiring to set off bombs and conspiracy to murder.

One of them, Cheung Chun-fu, had earlier pleaded guilty to charges of possessing explosives and firearms and was given an 18-month prison sentence.

The prosecution had told the court that the bomb plot involved planting explosives in Wan Chai during a rally to mark International Human Rights Day in December 2019.

Speaking to reporters, chief superintendent Steve Li from the national security police said he would not comment on the court's decision, but stressed the case was very serious in nature.

"This is a very serious case, involving genuine firearms, explosives, and a very organised plot to kill police and other innocent people as well," he said.

"But as a police, I can assure that we have tried our best to protect our society."