A customer leaves as an employee pulls down the shutters at a convenience store normally open 24 hours a day in Hong Kong. Photograph: Mohd Rasfan/AFP via Getty Images
Lam put out a pre-recorded video message, accusing protesters of half-paralysing the city, and plunging it into a very dark night. Flanked by all her ministers, who stood silent as Lam spoke, she called on the citys 7.5 million citizens to back her.
The extreme violence clearly illustrated that Hong Kongs public safety is widely endangered, Lam said, in her first comments since Fridays ban.
Crowds had taken to the streets soon after she announced the ban, effective overnight. Face masks have become a staple at protests, partly because of heavy teargas use and partly because people fear arrest or retaliation if they are identified.
Peaceful protesters form human chains after mask ban in Hong Kong video
Protesters set fire to two metro stations and vandalised shops and businesses considered pro-China; police responded with teargas, and a 14-year-old student was shot in the thigh with a live round. He was taken to hospital in a serious condition.
On Saturday, police sent text messages urging the public to avoid protests over the three-day weekend. But despite the transport difficulties, and the fact that Sundays protest had not got a police permit, large numbers were expected to turn out.
Secondary school students also launched a petition, calling on police not to punish or report them for wearing a mask.
The Chinese ambassador to the UK said Beijing would not hesitate to intervene if it thought it was necessary. Despite the worst outbreak of violence yet over the last week, and the shooting of two teenage students with live ammunition, he claimed the situation had improved and denied Lam had lost control.
Carrie Lam (C) stands with her cabinet as she delivers a video message released to media organisations in Hong Kong. Photograph: Handout/AFP via Getty Images
If the situation in Hong Kong becomes uncontrollable by Hong Kong government, the central government will not sit on their hands and watch, Liu Xiaoming
told the BBCs Newsnight. He added: (At present) the situation is still under control and we have full trust in the Hong Kong government and the chief executive.