At least a quarter of the 28,000-strong police force will turn out to handle the possible chaos should the Occupy Central movement for democracy carry out its threat to block streets in the main business hub later this month, sources close to the matter say.
The deployment would be the largest police operation since the city mobilised 9,000 officers during six days of World Trade Organisation meetings in 2005.
It would also be a near doubling of the police numbers deployed during the July 1 democracy march this year and the overnight sit-in on Chater Road on July 2.
The police plans come amid warnings by Occupy organisers in recent days of bringing Central to a standstill should the National People's Congress Standing Committee arrive at a framework for the 2017 chief-executive election later this month that does not offer a genuine choice of candidates for voters.
While police vacated their posts to converge on Central, the force would assign about 1,000 auxiliary officers and hundreds of retired officers - recently hired as station assistants - to maintain normal policing services, sources said.
The Police College in Wong Chuk Hang will be turned into a temporary detention centre, with room for 3,000 prisoners.
One police source said the force was discussing whether the Correctional Services Department could provide a facility to house detainees.
"The move is to prepare for the event of mass arrests if our temporary holding centre fails to accommodate all detainees," he said.
The Transport Department would help plan traffic diversions if traffic was paralysed, while the fire services and paramedics would also be on standby.
Frontline officers had been told to cancel their leave on August 31, and during the Mid-Autumn Festival from September 7 to 9, another police source said.
It is understood that 7,000 to 8,000 officers would be involved - including the entire police tactical unit (PTU) and officers from traffic divisions, patrol sub-units and emergency units.
PTU teams are expected to be on standby at various positions in Central. "They will swoop into action if radical activists try to paralyse traffic on major roads or occupy infrastructure," another source said. "We are preparing to deal with any eventuality."
The organised crime and triad bureau will also be involved.