Chief executive Carrie Lam invoked a colonial-era emergency law in a bid to quell months of anti-government unrest.
The ban comes after an escalation of violence during protests on 1 October, when an officer shot a demonstrator.
Reports on Friday said a 14-year-old had been shot in the leg.
He is reportedly being treated at Tuen Mun hospital and is in a serious condition.
A police statement published by the South China Morning Post confirmed an officer "fired one shot as his life was under serious threat" after being attacked by a large group of protesters, including with petrol bombs. The statement does not however say if anyone was hit.
The demonstrations have now died down throughout most of the territory, although there are still pockets of unrest.
Protests erupted immediately after the ban was announced.
Many left work early to join the spontaneous demonstrations. Some furious protesters blocked roads, torched Chinese flags and vandalised stations and businesses, as police fired rounds of tear gas.
The territory's Mass Transit Railway (MTR) announced a full service suspension of all trains, which will continue on Saturday morning until an assessment can be carried out.
A spokesman told the BBC this was due to vandalism and attacks on staff. Images showed fires lit at stations, and reports suggest a train was set ablaze.
Many Hong Kongers were forced to walk home amid the unrest.
Mask-wearing activists had also earlier called on others to wear masks in defiance of the government, which critics fear is becoming increasingly authoritarian.
Ms Lam said she was forced to implement the colonial-era law because violence at the now-weekly protests was "destroying the city", and she could not allow the situation "to get worse and worse".