Three leaders of Hong Kong's 2014 pro-democracy Occupy movement, which paralyzed parts of the Chinese-ruled city for nearly three months, denied public nuisance charges on Monday as international criticism of the erosion of civil liberties grows.

Law professor Benny Tai, 54, retired sociologist Chan Kin-man, 59, and retired pastor Chu Yiu-ming, 74, face charges of conspiracy and incitement to commit public nuisance, and incitement to incite public nuisance.

The closely watched trial illustrates the tensions in the former British colony as disaffected democracy activists push back against attempts by Communist Party leaders in Beijing to tighten their grip on the city's freedoms and autonomy.