Small groups of pro-democracy demonstrators remained on Hong Kong's streets Tuesday after protest leaders agreed to talks with the government and students returned to school for exams.

Talks between the government and student leaders are progressing at a snail's pace, although even protest organisers are now acutely worried that further disruption could alienate supporters.

The mass demonstrations to demand fully free elections have brought parts of Hong Kong to a standstill for more than a week, and while many in the city remain supportive of the movement, they also want to resume their daily lives.

Students held a third round of "preparatory talks" with government officials on Tuesday night in a bid to set conditions for formal negotiations.

A senior government official said full talks were earmarked for Friday afternoon between students and Chief Secretary Carrie Lam, the deputy to Hong Kong leader Leung Chun-ying.

"The dialogue, date and time have been decided. We tentatively set it at 4 pm on Friday," deputy secretary for constitutional and mainland affairs Ray Lau told reporters.

The pro-democracy organisers had agreed to talks earlier with Lam but called them off last Friday after what they described as "organised attacks" on protesters at the Mong Kok demonstration site.

One Hong Kong delegate to China's rubberstamp parliament said the demonstrations would not overturn Beijing's August decision to vet candidates for the city's 2017 leadership elections.

"I don't see why the National People's Congress Standing Committee would change its decision... It was a nationwide decision and the decision has to face the country's 1.3 billion people," Rita Fan told reporters.

- Back to study -

Tuesday saw another day of traffic mayhem, with diversions still in place causing nose-to-tail jams and commuter frustration, truncated bus routes and the reopening of primary schools adding to the chaos.

Police urged "students, onlookers and others" to leave the Mong Kok protest site, which has seen violent clashes.

"People holding different and strong views living in the area are highly emotional... The chance of further confrontations is increasing," senior superintendent Hui Chun-tak told reporters on Tuesday.

The few protesters that remain are still determined to make their point -- although they are unsure of the result.

"To be honest, I don't have confidence that we can succeed. But whether we succeed or not, I am giving my best. I also learned that we can speak out when it is needed," said Dickson Yeung, 20, who works as a customer relations officer.

"I still have hopes that we can achieve our goal of having true democracy," said May Li, a 19-year-old university student who has been protesting at the Admiralty site for a week.

But, she added, she was headed back to class to prepare for exams.

"I skipped classes completely last week. Except resting for a day or two, I have been staying here all day long. But this week I am going to classes. Mid-term tests are coming," she said.

- Parliament opening postponed -

Numbers of demonstrators slowly swelled throughout the day at the protest sites and outside the central government offices but remained far lower than during the peak demonstrations days earlier.

At the main site outside government headquarters early in the evening, an AFP reporter saw a small group of government loyalists sporting blue ribbons shouted down by pro-democracy demonstrators.

Otherwise the atmosphere was calm at the protest sites.

Yet despite dwindling crowds, the opening of the city's de-facto parliament scheduled for Wednesday was postponed to next week.

"I am not assured that there is a quiet and safe environment in the surroundings for a meeting to be held," Legislative Council president Jasper Tsang said.

"We do not easily change meeting schedules. It is a very special situation at an extraordinary time."

Democratic lawmakers slammed the cancellation.

"You can't dodge it forever. Even if you postpone it for three weeks, public anger will not go away," Civic Party Alan Leong told reporters.