* Hong Kong awaits campus showdowns between protesters and police
* Hong Kong, China condemn attack on justice secretary in London
* Thousands arrested since protests escalated in June
HONG KONG, Nov 15 (Reuters) - Hong Kong pro-democracy protesters partially unblocked a key highway on Friday and then blocked it again during the evening rush hour, exposing splits in a movement that has been largely leaderless in months of often violent unrest.
The Tolo highway runs along the side of the leafy campus of Chinese University. Protesters blocked it this week and clashed with police, throwing debris and petrol bombs on to the road linking the largely rural New Territories with the Kowloon peninsula to the south.
They turned the campus into a fortress, stockpiled with petrol bombs and bows and arrows as in several other universities, amid some of the worst violence in the former British colony in decades.
But many left after some of them allowed the partial reopening of the highway on Friday, taking others by surprise.
"I am disappointed about the decision to reopen the Tolo highway and its not our consensus," one student who gave his name as Cheung, 18, told Reuters.
"I was asleep when they had closed-door meetings. I was worried and scared after I realised what had happened and most protesters had left. I was worried the police might storm in again because so few people are left. Some protesters from the outside have gone too far.
Chinese University president Rocky Tuan said in an open letter that all outsiders must leave.
"Universities are places to study, not to resolve political disputes, or even a battlefield to create weapons and use force," he said.
"If the university cannot continue to fulfil its basic mission and tasks, we must seek the assistance of relevant government departments to lift the current crisis."
The highway closed again on Friday evening after its partial reopening and the Cross-Harbour Tunnel, outside the barricaded Polytechnic University where protesters have practised firing bows and arrows and throwing petrol bombs in a half-empty swimming pool, remained shut.
Students and protesters, who have barricaded at least five campuses, were burning makeshift roadblocks at Chinese University.
Remaining Chinese University students hunkered down on the bridge over the Tolo highway, black pirate-style freedom flags flying from lookout posts. A few on ladders with binoculars kept watch over the road.
There were only about 200 protesters there on Friday compared to at least 1,000 two days ago. There were also clashes with police in the Kowloon district of Mong Kok, one of the most densely populated areas on Earth.
The week has seen a marked intensification of the violence.
A 70-year-old street cleaner, who had been hit in the head by one of several bricks police said had been thrown by "masked rioters", died on Thursday. On Monday, police blamed a "rioter" for dousing a man in petrol and setting him on fire. The victim is in critical condition.
On the same day, police shot a protester in the abdomen. He is in stable condition.
"We can no longer can say Hong Kong is a safe city," Chief Secretary for Administration Matthew Cheung told a briefing.
Protesters are angry at perceived Chinese meddling in the city since it returned to Beijing rule in 1997 under a "one country, two systems" formula guaranteeing its colonial-era freedoms.
China denies interfering and has blamed Western countries for stirring up trouble.
Police have kept their distance from the campuses for more than two days, saying both sides should cool off, but many observers are afraid of what will happen if and when they move in.
China and Hong Kong both condemned an attack in London on Thursday by a "violent mob" on Hong Kong's justice secretary, the first direct altercation between demonstrators and a government minister.
Secretary for Justice Teresa Cheng, who was in London to promote Hong Kong as a "dispute resolution and deal-making hub", was targeted by a group of protesters who shouted "murderer" and "shameful".
The Hong Kong government said Cheng suffered "serious bodily harm" but gave no details. The Chinese Embassy in Britain said Cheng was "besieged and attacked by dozens of anti-China and pro-independence activists".
The British police said a woman had been taken to hospital with an injury to her arm and that they were investigating but no arrests had been made.
The unrest poses the gravest popular challenge to Chinese President Xi Jinping since he came to power in 2012. Xi said in Brazil on Thursday stopping violence was the most urgent task for Hong Kong.
The demonstrations have battered the retail and tourism sectors, with widespread disruptions across the financial centre and no end in sight to the violence and vandalism.
Hong Kong sank into recession for the first time in a decade in the third quarter, government data confirmed on Friday, with its economy shrinking by 3.2% from the previous quarter on a seasonally adjusted basis.
Video footage obtained by Reuters of the Chinese People's Liberation Army garrison headquarters near Hong Kong's Central business district showed more than a dozen troops conducting what appeared to be anti-riot drills against people pretending to be protesters carrying black umbrellas.
The PLA has stayed in the barracks since 1997 but China has warned that any attempt at independence will be crushed. (Reporting by Donny Kwok, Felix Tam, Twinnie Siu, Jessie Pang, Anne Marie Roantree and Marius Zaharia Writing by Anne Marie Roantree and Nick Macfie Editing by Robert Birsel and Philippa Fletcher)