Published: 2019-07-15 14:22:23 BdST
Lam made the comments at a hospital where three police officers were being treated for injuries sustained in skirmishes on Sunday with demonstrators angry about a controversial extradition bill.
Hong Kong has been rocked by large and sometimes violent street protests over the past month to oppose the extradition bill, plunging the former British colony into its biggest political crisis since it was handed back to China in 1997.
On Sunday, an afternoon protest march attended by tens of thousands of people ended in chaos in a shopping mall, where scores of protesters threw umbrellas and plastic bottles at police who retaliated by firing pepper spray and swinging batons.
Lam said more than 10 police were injured in skirmishes on Sunday, with six hospitalised.
"We thank the police officers for maintaining social order loyally and professionally, but they have suffered in attacks from those rioters - they can be called rioters," she said.
The government information office said 28 people, including police, were injured in the latest protest.
Police Chief Stephen Lo said late on Sunday more than 40 people were arrested for charges including assaulting police and illegal assembly.
The extradition bill that sparked the protests would have allowed criminal suspects in Hong Kong to be sent to China to face trial in courts controlled by the ruling Communist Party.
Critics of the bill say that would threaten Hong Kong's rule of law and its place as an Asian financial hub.
Demonstrations have drawn hundreds of thousands of people into the streets since early June.
Under pressure, Lam suspended the bill in mid-June and last week declared it "dead", but opponents say they will settle for nothing less than the formal withdrawal of the bill from the legislative process.
Protesters have recently seized upon the widespread anger over the bill to draw attention to a litany of other issues, including the territory's relative lack of democracy and border traders from mainland China.
They have also taken the movement out of the main business and government district on Hong Kong island to other spots around the territory, including the town of Sha Tin where the protest march and clashes happened on Sunday.
Hong Kong returned to Chinese rule in 1997 under a "one country, two systems" formula that guarantees its people freedoms for 50 years that are not enjoyed in mainland China, including the liberty to protest and an independent judiciary.
Beijing denies interfering in Hong Kong affairs, but many residents worry about what they see as an erosion of those freedoms and a relentless march toward mainland control.