The soldiers, unarmed, dressed in olive T-shirts with a Chinese flag on the sleeves, used buckets and brooms for about one hour to clean up streets around the barracks in Kowloon Tong, RTHK said.
One PLA soldier told the South China Morning Post that their actions weren't related to any direct orders from the Government of Hong Kong.
"We initiated this! 'Stopping violence and ending chaos' is our responsibility," he said, quoting a phrase used by President Xi Jinping.
So far, there hasn't been any official statement from the Government of Hong Kong about PLA soldiers on the streets.
According to Article 14 of the Garrison Law, PLA soldiers are permitted to enter the streets of Hong Kong to assist with disaster relief or maintaining public order if requested by the local government.