HONG KONG (BLOOMBERG) - Mainland Chinese students studying in Hong Kong are fleeing across the border to Shenzhen as protesters wage an ongoing battle with police that's turned the grounds of one top university into a smoking battlefield.

They are being helped to escape the Chinese University of Hong Kong (CUHK) - the site of the most serious confrontation between police and protesters this week - by supportive Chinese nationals and China's Communist Youth League.

Twelve hostels in Shenzhen are offering free accommodation for seven nights to mainland students enrolled in Hong Kong universities, in an initiative organised by the Shenzhen Communist Youth League, while mainland alumni groups are sponsoring taxis to drive students to the border crossing.

The strife ripping through Hong Kong, which spilled into open violence this week, has alarmed the city's mainland-born residents, who feel targeted by the anti-Beijing movement.

More than a million mainlanders, including many professionals, have migrated across the border since China regained control of the former British colony in 1997, helping swell Hong Kong's population to 7.5 million.

CUHK undergraduate Leo Lin left his dormitory at 4.30am on Wednesday morning (Nov 13) after seeing police firing tear gas and student protesters throwing petrol bombs for hours, joining what he says are thousands of other students who have fled.

"I didn't want to leave at the beginning. I wanted to go to classes today," said the 19-year-old. "But the atmosphere deteriorated quickly, and I suddenly felt the urge to leave."

Mr Lin took a taxi arranged by a mainland alumni group and is now in Shenzhen, where he plans to share an apartment with four to five friends for around 100 yuan (S$19.40) each per night.

They plan to stay in Shenzhen until Sunday, hoping that the situation calms down enough for them to return. Final examinations are in December.

Related Story Flash mob wreaks havoc in heart of Hong Kong financial district; universities emerge as new battleground

Related Story Continued chaos on Hong Kong roads due to strikes; all schools shut on Thursday

Related Story Worsening Hong Kong violence could embolden hawks in China

Related Story Fears mount as Hong Kong protesters hit Chinese businesses

By Mr Lin's estimation, only about a hundred mainland undergraduates still remain on the CUHK campus. Students from City University and the Hong Kong University of Science and Technology have also fled, he said.

The protests began in opposition to a since-scrapped government Bill allowing extraditions to mainland China and have expanded to include calls for greater democracy and an independent inquiry into police tactics.

While demonstrations started off largely peaceful, a radicalised flank which emphasises a darker, anti-China tone is now the most visible. Some demonstrators have burned Chinese flags and spray-painted the phrases "Chinazi" and "Hong Kong is not China!" across the city.

A Hong Kong Polytechnic University student, who gave his first name as Bruce, left the city on a high-speed train on Tuesday evening.

The 21-year-old said he was concerned for his safety, and needed a quiet place to study and complete his final-year project. He is now in a hotel in Shenzhen and his anxious parents have booked train tickets to join him.

"The moment I went through customs, I felt relaxed," he said. "At school, my muscles were tense."