An average of more than 110,000 vehicles pass through the tunnel each day, according to the Transport Department. An estimated 20 bus routes run through the tunnel moving many thousands of passengers between many areas on both sides of the harbor.

The blockade by protesters stopped all traffic through the tunnel for around 45 minutes.

In statements issued after 5 pm, the police warned protesters who strayed from the approved routs that they were participating in an illegal assembly.

They appealed to protesters not to obstruct roads road and the tunnel, and respect other people's rights while expressing their views.

The police noted that protesters have removed roadside railings to set up barricades at various road junctions along Nathan Road, seriously obstructing traffic and hindering emergency services.

In a police briefing on Saturday morning about arrangements for the planned protests in the coming three days, Senior Superintendent (Operations) of Kowloon West Cheung Wai-wah stressed that the police have noted that there were online messages advocating the storming of police cordons.

He reiterated that the police had "zero tolerance" on violence and would take resolute actions against any violent act.

In the past several weeks, various protests that started off peacefully had deteriorated into violent clashes with the police. Last Sunday, a gathering in a park spilled over illegally into the streets ending in a violent confrontation that turned part of the western Hong Kong Island into a war zone.