The Hong Kong police arrested 1,377 people said to have been involved in violent incidents during the Hong Kong Polytechnic University (PolyU) standoff, officers told a news conference on Friday.

The police said a search of universities in the city found nearly 10,000 petrol bombs. In the most recent operation, 12 officers were injured. A total of 483 officers were injured over the whole security operation.

A total of 5,890 people have been arrested amid the unrest in the Hong Kong Special Administrative Region (SAR), including 4,368 males and 1,522 females, on various charges, including unlawful assembly, possession of an offensive weapon and criminal damage, according to the police.

Since the beginning of November, Hong Kong's universities have been occupied and damaged. In some cases they became weapons arsenals for protesters.

Last week, rioters attacked the Chinese University of Hong Kong (CUHK) and threw debris onto the street, leading to road closures.

When the rioters left CUHK, they dispersed to different universities, making petrol bombs at PolyU and burning a toll station at the Cross-Harbor Tunnel.

"The police have taken control of the PolyU area to prevent further damage. We always hope to resolve this issue peacefully and flexibly," said the police.

The Hong Kong police have returned the PolyU to school officials. The handover came after about two weeks of siege, where some protesters were believed to remain on campus. The university president called for a peaceful solution to the crisis.

"We must look for the opportunity for a peaceful solution because I believe violence cannot solve any problems," President Teng Jin-guang said.

"We can have different political standings, we can have different perspectives of issues, but we should talk to each other peacefully, and exchange our views rationally. And this is my sincere wish for Hong Kong and for this university."

Violent incidents have damaged a total of 730 sets of traffic lights in various districts of the Asian financial hub since June, official data showed Thursday.

After months of repair works, most of the traffic lights have resumed normal operation, except 80 sets under urgent repair.