HONG KONG, Nov. 18 (Xinhua) -- A senior government official of China's Hong Kong Special Administrative Region (HKSAR) on Monday expressed most severe condemnation of rioters' intensifying violence and called on all people to keep restraint and say "no" to violence.

Over the past week in multiple areas of Hong Kong, intense clashes erupted again as rioters continued to escalate their violence, in particular the fierce clash taking place at the Hong Kong Polytechnic University (PolyU), said Chief Secretary for Administration Matthew Cheung at a joint press conference that was also attended by three other secretaries.

From Sunday afternoon, mobsters gathering around the PolyU have launched assaults on police officers using lethal weapons including petrol bombs, bows and arrows, metal balls and bricks, challenging the bottom line of the police, said Cheung, adding two police officers were hit by rioters' arrow and metal ball respectively.

"Such extreme violence posed grave threats to the life of everyone at scene, including the press on site," Cheung stressed.

The rioters even set alight the footbridge linking the PolyU campus and Mass Transit Railway (MTR) stations and part of the footbridge near Cheong Wan Road towards Tsim Sha Tsui East, which threatened the safety of people on the spot, Cheung said.

Cheung appealed to the rioters inside the PolyU campus to follow the police's instructions and leave the university, while urging citizens not to get close to the campus so as to avoid further chaos.

On public transport conditions, Cheung said that the East Rail Line and Cross-Harbor Tunnel, which were most severely damaged, haven't resumed normal operation. Traffic disruption not only affects commute, school, travel and commerce, but also impedes emergency medical services and social services, he noted.

Cheung strongly called on people from all walks of life in Hong Kong to keep calm and draw a clear line with violence in a bid to bring the society back to peace, adding that violence must be stopped to let the district council elections scheduled for Nov. 24 be conducted in a peaceful, rational and orderly manner.