A heavily-fortified university campus in Hong Kong has been stormed by police with some declaring it a “war zone”.

Police stormed the Hong Kong Polytechnic University before dawn on Monday where anti-government protesters had barricaded themselves behind sophisticated and elaborate walls.

They had been fighting back using catapults, petrol bombs and bows and arrows — one of which landed in the leg of a police officer, reportsnews.com.au.

The ABC’s China correspondent, Bill Birtles, is in the thick of it and says “all hell is breaking loose”.

In a series of tweets from the ground, Birtles wrote that police had blocked all roads and exits around the university and arrested those who were trying to administer first aid.

“The saddest photo of the night,” he wrote alongside a picture of volunteers with their wrists tied together behind their backs. (NAN)