It's Hong Kong's biggest national security case under a Beijing-imposed law that crushed a once-thriving pro-democracy movement.

A Hong Kong court will sentence dozens of former democracy advocates in the city’s largest national security trial, a move likely to further deter dissent in the finance hub and attract condemnation from Western governments.

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.