TV footage showed medical personal attending to the young male on Tai Ha Road. Sources said he was a form five student from Tsuen Wan.
He appeared to have been shot in the chest, but was conscious as he was taken to hospital.
Other footage of the incident circulating online shows the boy was part of a group of protesters who were apparently using rods and sticks to beat an officer on the ground when another policeman approached with his pistol out.
Some of the protesters attacked the approaching officer, who fired at what appeared to be point blank range. No warning shot could be heard on the video.
Other protesters then hurled a petrol bomb at the police, who then apparently withdrew.
The video also shows the injured protester yelling out “My chest hurts a lot”, along with his full name and identity card number as volunteer first-aid workers attempted to help him as he lay bleeding on the pavement.
Meanwhile, live rounds were heard in Yau Ma Tei after protesters surrounded a group of officers and began beating them.
TV footage showed at least two officers with blood pouring down their faces as they retreated into a van. A Molotov cocktail was then thrown at the vehicle, prompting officers to get back out to tackle the group again.
An officer was beaten after falling down and two shots then rang out.
Riot police were seen pointing their guns at protesters at close range and the crowd then fled towards Nathan Road.
Two masked men in plain clothes were seen joining the police in their van before it also left the scene.
The Hospital Authority said that by around 5.30pm, 15 injured people had been taken to hospital.
Last updated: 2019-10-01 HKT 19:04