Presidents of nine Hong Kong universities have called for an immediate political solution to restore safety and public order in the city, where multiple campuses "are now under protesters' control." 

In a statement, the leaders said violence had rapidly escalated in Hong Kong this week and some staff and students had left campuses out of fear for their safety.

President of the Chinese University of Hong Kong (CUHK) Rocky Tuan, one of the nine presidents, said in an open letter on Friday that rioters' days-long occupation had turned the campus into a "terrorist base." He demanded that all outsiders leave the campus immediately as the university was not a "battlefield" to make and use weapons.  

"Our university has been occupied by masked men, including those from outside the university, and the situation has been completely out of control and is unacceptable," Tuan said in the letter published on the university's website.

Chief Secretary for Hong Kong Special Administrative Region (HKSAR) Matthew Cheung also condemned the situation during an inter-departmental press conference on Friday. 

Several college campuses were occupied by rioters including the CUHK, where about 400 petrol bombs were thrown. Rioters were reportedly creating deadly weapons such as petrol bombs inside universities and blocking accesses to the campuses, Cheung said. 

The HKSAR government will take necessary actions to ensure people's safety and their rights to travel to the best of its ability, Cheung stressed. 

Masked rioters started to wreak havoc on the CUHK campus in Sha Tin in the New Territories on Monday. Objects were repeatedly dropped from a bridge over Tolo Highway to obstruct traffic on a carriageway, seriously obstructing emergency services and the movement of residents in the New Territories. 

According to HK police, the carriageway blocked by rioters was partially reopened on Friday noon.