Unlawful street assemblies in Hong Kong that halted traffic were described by the city's leader on Wednesday as a plot hatched more than a year ago that went out of control when put into operation.

The idea of pushing the central government to accept an electoral reform package by setting up blockades in the heart of Hong Kong first emerged in January 2013.

The initiator, law professor Benny Tai Yiu-ting, soon turned the idea into an advocacy group.