A standoff continued Wednesday between anti-government protesters holed up in a Hong Kong university and police who have surrounded the campus.

Dozens of defiant protesters remain barricaded inside Polytechnic University in Kowloon, with many remaining inside to avoid arrest while preventing the police from entering.

Nearly 900 people have since Sunday turned themselves in to police, including some 300 minors, Security Secretary John Lee said. He urged protesters still inside to surrender while reiterating that they will be arrested for rioting.

"We have to tell everybody still remaining on the campus that, first of all, it will be dangerous for them to remain, and...if they contravene the law they have to face the consequence of the law," Lee told reporters.

The Hung Hom Cross Harbor Tunnel, one of three major tunnels connecting Hong Kong Island and Kowloon, remained closed to traffic early Wednesday. The tunnel entrance, which is close to the university campus, has been blocked by debris laid by protesters since last week.

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A 15-year-old high school student, one of some 60 protesters remaining in the campus, said he is staying to ensure the safety of others.

"I didn't expect a lockdown," the teen said. "I feel calm, I am not anxious to leave and not regretting having come to Poly U. Of course, I am scared about being arrested, but still I will stay until (the police) come arrest me."

He pleaded for the public's understanding of the students' actions, insisting that it is the government which initiated the violence.

Meanwhile, another campaign aimed at disrupting road and rail services was launched Wednesday as most schools resumed normal operation.

Subway services were temporarily delayed during rush hour, stranding commuters and forcing some stations to be closed. Road blockages in Kowloon's Kwun Tong district by student protesters also stopped traffic and led to minor scuffles among road users and the protesters.

The protests, sparked by a now-withdrawn bill that sought to allow extraditions to mainland China, have been ongoing since June, plunging Hong Kong into its most serious political crisis since its handover to Chinese rule in 1997.