Hong Kong's High Court on Tuesday jailed a leading pro-democracy activist for 10 years at the start of sentencing in a years-long national security trial that has damaged the city's once feisty pro-democracy movement and drawn global criticism.

A Hong Kong court sentenced former democracy advocate Benny Tai to 10 years in prison, the longest sentence ever meted out using a China-imposed security law, in a move likely to further deter dissent in the finance hub and attract condemnation from Western governments.

A Hong Kong court on Tuesday jailed all 45 defendants convicted in the city's largest trial under its sweeping national security law, with "mastermind" Benny Tai receiving the longest term