"I appeal to the protesters, who have been illegally occupying roads, to pack up their belongings and to leave the protest sites in the next 20 hours," Lam told the press.
The official advised demonstrators to avoid "unnecessary confrontation" with the police, who will be clearing the camp on Thursday, adding that law enforcement will take immediate action against anyone who opposes the process.
Hong Kong's Occupy Central campaign began in September, following Beijing's decision to vet candidates running in the 2017 Hong Kong Chief Executive election. Pro-democracy activists flooded the streets, blocking roads and demanding free elections. The protests have led to numerous arrests and clashes with police.
In 1997, the United Kingdom transferred Hong Kong's sovereignty to China, ending over 100 years of British rule. Hong Kong is an autonomous administrative region, granted economic, legal and political autonomy from Beijing under the "one country, two systems" principle.