Protests in Hong Kong once again reached a crescendo very early Sunday morning as protestors hurled petrol bombs at police who shot tear gas canisters in return, Reuters reports.

The riot happened near Hong Kong Polytechnic University in Kowloon district.

Unrest has rocked the former British colony for upwards of five months, but some believe that soldiers from China’s People’s Liberation Army (PLA) cleaning debris in the streets earlier in the day could've stoked an already tense situation.

The clean-up effort by the PLA, dubbed “voluntary community activity” by the Chinese military, was not requested by the Hong Kong, according to Reuters.

It was only the second time since Hong Kong returned to Chinese rule in 1997 that Chinese troops have been present on the street in the city.

Until this point, the soldiers have remained inside their barracks during the unrest.