Hong Kong police on Friday lifted a cordon around a university campus that became a battleground for anti-government protesters holed up inside during a 13-day siege, Eurasia Diary reports citing Deutsche Welle.

Police left Hong Kong Polytechnic University after they entered the campus a day earlier to collect evidence and remove dangerous items.

In a statement, police said that over two days they had seized 3,989 gasoline bombs, 1,339 explosive items, 601 bottles of corrosive liquids and 573 weapons. No protesters were left inside the campus.

Roughly 1,000 protesters had retreated inside the campus after battling police on nearby streets on November 17, leading to a violent standoff that left the university ransacked.

Police said 700 people were arrested and the details of 300 minors were recorded. Some protesters were able to escape. 

The university now faces the daunting task of cleaning up the campus.

In a letter to students on Friday, university officials called on people to stay away.

"The campus is still unsafe, and will continue (to) be closed," officials said.