Police officers gather forensic evidence at the campus of the Polytechnic University (PolyU) in Hong Kong, China, November 28, 2019. Hong Kong police entered Polytechnic University on Thursday after a two-week siege and said they were searching for evidence and dangerous items. The police emphasised to reporters at the scene that they were not searching for any protesters that may be still holed up on campus. REUTERS/Thomas Peter

Police officers examine forensic evidence at the campus of the Polytechnic University (PolyU) in Hong Kong, China, November 28, 2019. It was not clear whether any protesters remained at the site as a team of about 100 plain-clothed policemen and firemen moved into the sprawling campus to collect evidence and remove dangerous items such as petrol bombs. Police said any protesters found would receive medical treatment and arrests were not a priority. REUTERS/Thomas Peter

A police officer examines forensic evidence at the campus of the Polytechnic University (PolyU) in Hong Kong, China, November 28, 2019. Vice president of Hong Kong Polytechnic University, Ben Young, urged any remaining protesters to leave the campus due to its dangerous environment and hoped the campus can be reopened after the police search. REUTERS/Thomas Peter

Police officers examine forensic evidence at the campus of the Polytechnic University (PolyU) in Hong Kong, China, November 28, 2019. The university on the Kowloon Peninsula was turned into a battleground in mid-November, when protesters barricaded themselves in and clashed with riot police in a hail of petrol bombs, water cannon and tear gas. About 1,100 people were arrested last week, some while trying to escape. REUTERS/Thomas Peter

Police officers examine forensic evidence at the campus of the Polytechnic University (PolyU) in Hong Kong, China, November 28, 2019. More than 5,800 people have been arrested since the unrest broke out in June over a proposal to allow extraditions to mainland China, the numbers increasing exponentially in October and November as violence escalated. REUTERS/Thomas Peter

Police officers examine forensic evidence at the campus of the Polytechnic University (PolyU) in Hong Kong, China, November 28, 2019. Hong Kong police entered Polytechnic University on Thursday after a two-week siege and said they were searching for evidence and dangerous items. The police emphasised to reporters at the scene that they were not searching for any protesters that may be still holed up on campus. REUTERS/Thomas Peter