A protester makes a gesture during a protest on June 12, 2019 in Hong Kong China. Large crowds of protesters gathered in central Hong Kong as the city braced for another mass rally in a show of strength against the government over a divisive plan to allow extraditions to China. Anthony Kwan/Getty Images

Hong Kong leader Carrie Lam has invoked colonial-era emergency powers and banned facial coverings as a "deterrent" against violent protests which have rocked the city for four months.

At a press conference on Friday, Lam said her decision to ban face masks was necessary as protests have caused "serious public danger."

The ruling, which takes effect on Saturday, bans facial coverings that include "a mask or any other article of any kind (including paint) that covers all or part of a person's face" as part of an "unlawful assembly," or at a public meeting or procession.

The ban follows a spike in violence over the weekend in response to the five-year anniversary of the Umbrella Movement on September 28, and the 70th anniversary of the formation of the People's Republic of China on October 1.

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Hong Kong leader Carrie Lam on Friday invoked colonial-era emergency powers and banned face masks as protests in the city turn increasingly violent.

At a press conference, Lam said her decision to ban face masks was necessary as protests have caused "serious public danger."

"As the current situation has clearly given rise to a state of serious public danger, the Chief Executive and council decided at a special meeting this morning to invoke the power under the emergency regulations ordinance, and make a new regulation by the name of Prohibition on Face Covering Regulation, which is essentially an anti-mask law."

She added that she believed the regulation would create a "deterrent" against protesters who have adopted a uniform of face coverings and helmets in order to hide their identities.

"This is something which has already been introduced in a number of jurisdictions around the world and [has been] discussed here in Hong Kong. We believe that the new law will create a deterrent effect against masked violent protesters and rioters, and will assist the police in its law enforcement."

Read more: Barricades, human chains, and battling tear gas: We followed Hong Kong activists through the city's most turbulent protests yet

The new law will take effect on Saturday, and will prohibit facial coverings include "a mask or any other article of any kind (including paint) that covers all or part of a person's face" as part of an "unlawful assembly," or at any public meeting or procession.

Those who violate the law could face a fine of up to $HK25,000 ($3,100) and up to one year in prison.

Hong Kong Chief Executive Carrie Lam Cheng Yuet-ngor speaks at a news conference before the weekly Executive Council meeting on August 20, 2019 in Hong Kong, China. Mai Shangmin/China News Service/Visual China Group via Getty Images via Getty Images

Read more: An 18-year-old protester who was shot in the chest at point-blank range by Hong Kong police will be charged with assault

Professional, religious, or health reasons for a facial covering are exempt from the ban.

Large-scale demonstrations have taken place over the last week to coincide with the five-year anniversary of the Umbrella Movement on September 28, and the 70th anniversary of the formation of the People's Republic of China on October 1.

Clashes between police and protesters erupted across the city, and officers fired tear gas and water cannons at crowds.

On Tuesday, police shot 18-year-old protester Tsang Chi-kin at point-blank range in the chest, marking the first time that live fire was used since protests began in June.

A foreign journalist was also blinded after being hit in the eye with a rubber bullet on Sunday.