Dozens of foreign students have been urged to leave Hong Kong after another night of clashes left several people seriously injured.

A worker for the Food and Environmental Hygiene Department, struck by an object thrown by protesters earlier on Wednesday, was in critical condition, according to the government. A 15-year-old believed to have been hit in the head by a tear-gas canister has reportedly suffered a skull fracture.

A man dressed in black and around the age of 30 was found dead in Tsuen Wan in Hong Kong’s New Territories, according to police who said he appeared to have fallen from a building.

On Thursday, foreign students including mainland Chinese students were evacuating Hong Kong after several universities emerged as battlegrounds as protesters tried to prevent police from storming their campuses.

Several Nordic students at Hong Kong Baptist University were being moved after anti-government demonstrators moved on to its grounds, and the Technical University of Denmark (DTU) urged its 36 students in Hong Kong to return home.

Student Elina Neverdal Hjoennevaag told the Norwegian broadcaster NRK on Wednesday they were being sent to a hotel, adding: “I don’t really know what is happening. I must pack.”

She said she and several other exchange students were told to pack and move away, saying: “People walked out with their suitcases. Many cried.”

The Norwegian foreign ministry said on its website that “students should continuously evaluate campus safety if teaching is interrupted due to protests”.

Anders Overgaard Bjarklev, the head of DTU, said the decision to move came after some of the riots shifted to the campuses and “some of our students have been forced to move from their dormitories because they were put on fire”.

DTU would also resolve “any academic challenges associated with the interrupted course”.

Australia’s foreign affairs minister, Marise Payne, issued a statement calling on police and protesters to “exercise restraint and take steps to de-escalate tensions”.

“It is essential that the police respond proportionately to protests,” Payne said in a statement.

Police on Tuesday raided the Chinese University of Hong Kong, setting off violent clashes. The university remained barricaded by demonstrators on Thursday, with roadblocks and brick walls at the schools various entrances. Protesters also occupied a bridge that leads into the campus.

Police have accused the university of being a “manufacturing base for petrol bombs and a refuge for rioters and criminals” after some protesters fired burning arrows – taken from the university sports centre – at officers and threw 400 petrol bombs. Police fired more than 1,500 rounds of tear gas and more than 1,300 rubber bullets at the demonstrators. The city was paralysed, with much of its public transport suspended and all universities closed.

Several universities have cancelled classes for the rest of the semester or moved lectures online.

Hong Kong’s Education Bureau has suspended classes at primary and secondary schools for Thursday because of violence and described the situation in the city as “chilling”. The bureau also appealed for “school children to stay at home, not to hang around in the streets, to stay away from danger, and not to participate in illegal activities”.

Mainland Chinese students have also fled the unrest, taking advantage of a program that offers them a week of free accommodation in hotels and hostels in the neighbouring city of Shenzhen.

Chinese media reported that one hostel had received more than 80 applications for rooms by Wednesday morning.

The Beijing Evening News reported that protesters had broken into the dormitories of mainland students, spray-painting insults on walls and banging on doors.

Hong Kong police said on Wednesday that they had helped a group of mainland students leave their campus after it was barricaded by demonstrators.

Taiwan’s representative office in Hong Kong has reportedly helped 71 Taiwanese students return home.

The Taiwanese president, Tsai Ing-wen, called on Hong Kong’s government to cease “acts of repression,” saying such acts are threatening freedom and the rule of law.

Commenting on the police assault on students at the Chinese University of Hong Kong, Tsai tweeted that police in Taiwan used similar tactics during the years of martial law, which was lifted in 1987. She wrote: “Our dark past, which we have worked so hard to put behind us, has become the present reality for Hong Kong.”

China’s foreign ministry meanwhile again warned the US not to interfere with Hong Kong’s affairs, saying the city was part of China. Spokesman Geng Shuang said at a daily briefing on Wednesday that members of the US Senate should stop trying to promote bills on human rights or democracy in Hong Kong. “I want to reiterate that Hong Kong is China’s Hong Kong. Hong Kong affairs are purely China’s internal affairs and cannot be interfered by any external forces,” he said.