Police used numbing "pressure point tactics" to haul reluctant protesters away from their sit-in in Chater Road early yesterday.
They also divided the demonstrators into small groups to make them easier to control.
The tactics were revealed as the force came under fire for "needlessly" arresting more than 500 people in the absence of any violence or scuffles.
As columns of police reinforcements arrived at 1.30am, the demonstrators braced for pepper spray, water cannon or even tear gas.
But the force had a different game plan.
"Breaking them into small groups helped us control them better," a police source said. "Our vital concern was the safety of protesters and our officers."
Protesters were seen being lifted off the ground, sometimes by as many as four or five officers. Others were taken away in wheelchairs. All were loaded onto coaches and shuttled to the temporary detention centre at the Police College in Aberdeen.
Officers were seen covering protesters' mouths, twisting their necks and bending their elbows, drawing an outcry from students and onlookers.
But the police source said officers were just employing pressure point tactics.
"For those who defied our repeated orders to leave and refused to release their arms, officers controlled them by pressing their nerve points," he said.
This caused a temporary numbness and a tingling sensation so that officers could separate and remove them one by one.
"To prevent protesters putting up a struggle while being taken away, their hands were bent inward," the police source said, adding that this was to prevent them from falling on to the ground.
But Anson Chan Fang On-sang, convenor of think tank Hong Kong 2020 and a former chief secretary, criticised police handling of the situation.
"There wasn't any violence or scuffles. Why did police have to arrest more than 500 people?" she asked. "Police are giving people the impression that they are treating citizens as their enemies."
The operation began at 1.30am with the roar of police megaphones warning protesters in English that they were taking part in an unlawful assembly.
Journalists were also told to leave the area, but were then confined to pens, surrounded by police and unable to move freely in the protest grounds.
First to leave were the leaders of the movement, including Federation of Students secretary general Alex Chow Yong-kang, who sought to rally the protesters as the arrests were being made.
"You are violating the constitution! The whole world will know how ugly the Hong Kong police and government is!" he shouted to police before he was taken away. With the leaders of the protest gone, the officers moved in on the main body.
Most protesters put up only minimal resistance. Each time someone was removed, bystanders and fellow protesters shouted out the police officer's badge number and chanted "stop using violence".