HONG KONG — In a rare public intervention on the subject, Chinese President Xi Jinping said spiraling protests in Hong Kong were challenging the "one country, two systems" principle ruling the mainland's relations to the semi-autonomous region.

Halting the clashes and "controlling chaos" was the most urgent task facing Hong Kong officials, Xi said during a trip to Brazil on Thursday, adding that the “continuous violence and crimes are seriously jeopardizing justice and public safety."

Protests in the former British colony — which operates under the one country, two systems principle that allows it greater liberties compared to its mainland counterparts — were sparked six months ago by a controversial extradition bill. These quickly morphed into sometimes huge and violent demonstrations with broader demands for more democracy and police accountability.

Beijing denies it has interfered in Hong Kong's management of the months of spiraling violence, and instead blames the West for fomenting the protests that pose one of the most serious challenges to Xi since he came to power in 2012.

Xi's comments came the same day a 70-year-old hit by bricks police said had been thrown by "masked rioters" died.

Xi Jinping arrives for a meeting in Brasilia, Brazil, on Thursday. Pavel Golovkin / Reuters

Police have called the actions of the protesters "riotous" and called them "rioters," terms demonstrators contest.

Police said the man, whom they identified as "Luo," was believed to have been on his way to lunch when he was hit during a clash between protesters and local residents, police superintendent Chan Tin Chu told reporters.

“We believed that Luo was filming the scene when black-clad protesters began throwing metal rods and bricks at residents. Then somebody in black dashed forward and hurled a brick at his head,” Chan said.

Luo was found unconscious on the spot, taken to a hospital emergency room, and then later transferred to the neurosurgery high-dependency unit.

NBC News could not confirm the police's version of events.

Thursday's death capped a week of violence. 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.

On Tuesday, violence spiraled at the prestigious Chinese University of Hong Kong, as police were accused by protesters of charging onto the campus to detain demonstrators without letting the university know.

The university ended its semester early along with several schools and colleges.

Traffic disruptions and class suspensions have become routine for Hong Kong as protesters try to paralyze the city with flash mobs protests.

While white-collar workers have also been heeding online calls to “lunch together” every day — a euphemism for marching at lunchtime — universities have morphed into new battlegrounds where students barricade roads and trains using flaming arrows and catapults.