Talks with student leaders of a democracy protest that has blocked main roads in Hong Kong for nearly two weeks are off because they are unlikely to be constructive, a senior Hong Kong government official said.

Chief Secretary Carrie Lam said that the talks scheduled for Friday will not go ahead because they have been "seriously undermined" by remarks from the student leaders.

Her announcement came hours after student leaders called for supporters to redouble their efforts to occupy the main protest zone - a highway outside government headquarters that they are now dubbing Umbrella Square.

Thousands of protesters have occupied the thoroughfare since September 28, when police used tear gas in a failed attempt to disperse the crowd.

However, the number of demonstrators has dwindled sharply this week.

"I truly regret that we will not be able to have a meeting tomorrow which will produce any constructive outcome," Ms Lam said.

The protesters are demanding the government of the specially administered Chinese region abandon plans to allow Beijing to screen candidates for the city's inaugural elections for its leader in 2017.

They also want the current Beijing-backed leader, Leung Chun-ying, to resign.