HONG KONG (Reuters) - Hong Kong authorities started to clear the last of three pro-democracy protest sites on Monday, marking the end of demonstration camps in the city that have blocked streets for more than two months.

Around a hundred police swept into Causeway Bay, a bustling shopping district popular with mainland Chinese tourists, to remove barricades as protesters scrambled to pack up their belongings from the smallest of the three main sites.

One protester played the drums next to a cardboard cut-out of Chinese President Xi Jinping as onlookers stood by. About 10 people sat in the front line waiting to be arrested.

"I don't think it's a failure. This is not the end," said K.T Tang, a legal executive. "I hope the next time when we gather in the streets, we will be celebrating, instead of shedding tears for achieving nothing."

The mainly peaceful protests have represented one of the most serious challenges to China's authority since the 1989 pro-democracy demonstrations and bloody crackdown in and around Beijing's Tiananmen Square.

On Thursday, police cleared most of the main protest site in the Admiralty district next to government headquarters, arresting scores of activists in a largely peaceful operation.

That followed the clearance in late November of a site in Mong Kok, a gritty residential across the harbor from the main business district, a move that sparked several nights of running battles between demonstrators and police.

Hong Kong returned to Chinese rule in 1997 under a "one country, two systems" formula that gives the city more autonomy and freedom than the mainland and a goal of universal suffrage.

The protesters are demanding open nominations in the city's next election for chief executive in 2017. Beijing has said it will allow a 2017 vote but only between pre-screened candidates.

Protest leaders have said they will consider other forms of civil disobedience, given Beijing's continued refusal to grant any concessions.

As the dust settles on Hong Kong's pro-democracy 'Occupy' protests, China is likely to embark on a sweeping but covert campaign across the territory's judiciary, media and universities to ensure there is no recurrence, activists and politicians say.