Hong Kong will create its own national security law "as soon as possible", city leader John Lee said Tuesday, adding insurrection and other crimes not covered by existing legislation imposed by Beijing four years ago. 

Massive pro-democracy protests rocked the finance hub in 2019, bringing hundreds of thousands of people to the streets to call for greater freedoms. 

In response, Beijing imposed a national security law to punish four major crimes -- secession, subversion, terrorism and collusion with foreign foreign forces -- with sentences ranging up to life in prison. 

Officials on Tuesday said that Hong Kong's own security law -- mandated under Article 23 of the city's mini-constitution -- will cover five offenses, including treason, insurrection and espionage.

"I must stress that the Basic Law Article 23 legislation must be done... as soon as possible," Lee said. 

"This is a constitutional responsibility of (Hong Kong)... that has not been fulfilled 26 years after Hong Kong's handover," he said. 

Since the British handed Hong Kong back to China in 1997, the city has been under a "One country, two systems" regime, in which the legal and court structures are separate from the mainland.

Under its mini-constitution, known as the Basic Law, Hong Kong is required to make its own law combating seven security-related crimes, including treason and espionage. 

The last legislative attempt in 2003 was shelved after half a million Hong Kongers took to the streets to protest the move.