* Hong Kong protesters accuse police of brutality
* Police say officers told "not to succumb to emotions"
* Friday protest the first of many over a long weekend
* Joshua Wong expected to run in local elections in November (Adds Joshua Wong expected to run in local elections, paragraphs 14-15)
By Jessie Pang and Felix Tam
HONG KONG, Sept 27 (Reuters) - Thousands of Hong Kong protesters rallied at the harbour side on Friday, chanting slogans accusing the police of brutality and setting the stage for a weekend of demonstrations leading up to the 70th anniversary of the People's Republic of China.
The downtown rally was one of a series of protests that have united activists denouncing Chinese rule, calling for democracy and even for independence from Beijing, often resulting in violent clashes with police in the former British colony.
Activists have targeted police over more than three months with petrol bombs, rocks and laser shone in their eyes, furious at social media footage of random beatings, especially one night against protesters cowering on the floor of a subway train.
Police have responded with teargas, water cannon, rubber bullets and occasional live rounds fired into the air.
The protesters gathered at a park on reclaimed land in front of central government offices on Friday night calling for an investigation into the remote San Uk Ling camp near the Chinese border where they say detained protesters were abused, a claim police deny.
"It's obvious that there's a problem of police brutality," said 19-year-old university student Peter Sin. "They now arrest people randomly and there's much inhumane treatment during prosecution and detention."
Police said the camp was no longer being used to hold protesters.
"Its setting and facilities are all in line with police policies and regulations," they said in a statement. "We will stop using San Uk Ling Holding Centre for holding arrested people in this operation. The reason is to avoid any further public speculation and unnecessary remarks accusing the police."
One officer told reporters last week that some officers had overstepped the line when dealing with protesters.
"You are talking about a prolonged situation, chaos, violent encounters," he said. "We have established procedures to deal with allegations of abuse of force. Every day, with every chance we have, we remind our officers not to succumb to emotions.
"We've gone through multiple situations where lethal force would have been justified, but our officers chose not to use it."