Leung said the blockade of key parts of the Asian financial hub - now entering its third week - could not continue indefinitely.
Speaking in an interview with the local TVB television station, Leung said his government would continue to try to talk with student leaders but did not rule out the use of "minimum force" to clear the area.
The last few weeks had "proved that a mass movement is something easy to start, but difficult to stop," he said.
"And no-one can direct the direction and pace of this movement. It is now a movement that has lost control."
Leung also warned that there was "zero chance" that China's leaders in Beijing would change an August decision limiting democracy in Hong Kong, Reuters reported.
The former British colony was promised that its freedoms would be protected under a "one country/two systems" formula, when Britain handed its old colony back to China 17 years ago.
Beijing has said that only candidates screened by a nomination committee will be able to contest a full city-wide vote to choose the next chief executive in 2017.
The official People's Daily in Beijing described the so-called Occupy Central movement as "unrest" in a front-page editorial published on Saturday - language some analysts said reflected the growing unease among China's leaders.