Hong Kong protest leaders said late Monday they had agreed to hold talks with the government as their numbers dwindled and they faced growing pressure to end their pro-democracy sit-in.

The mass rallies that had drawn tens of thousands evaporated Sunday night in the face of a warning from Hong Kong's embattled leader Leung Chun-ying to leave the streets and allow government offices to reopen.

Many heeded the call but several hundred weary demonstrators remained at the main site in downtown Admiralty, with similar numbers across the harbour in Mongkok.

Student leaders denied their campaign for free elections had lost momentum, saying they would remain on the streets, even as they announced that talks with the government would take place this week.

But Leung issued another warning to disperse, saying they should leave the flashpoint district of Mongkok -- which has seen ugly scuffles with triad mobs -- "as soon as possible".

"To prevent violent crime and to reduce the amount of injuries, police will take action at the right time," Leung said in a televised address, describing the area as "high risk".

The protesters and their well-organised campaign have enjoyed strong public support, with sympathy soaring after police used tear gas on the crowds. But after shutting down parts of the city for more than a week, irritation has grown.

Highways were jammed with traffic and subway trains were packed Monday as frustrated commuters tried to find their way to and from work, battling cancelled bus routes and road diversions.

"They have to let the cars through as soon as possible -- they are blocking the way," 25-year-old Michael Lau told AFP as he travelled on the city's tram network.

- 'Don't affect our livelihoods' -

A four-day environment symposium gathering 11 Nobel winners that was due to open on Wednesday has been scrapped "due to the sustained disruptions in the city," the organisers said Monday.

However, secondary schools closures in affected areas, which had been a particular headache for families, were lifted and the government said primary schools would reopen on Tuesday.

"To demonstrate is one thing -- but don't affect our livelihoods any more, because we have rent to pay," said a fruit juice seller who gave her name as Mrs Hau.

But some backed the protesters.

"I don't mind the extra time I spend getting home. I support the students," Judy Kwan, a nurse, told AFP.

"Some of my family think it's a little annoying, but we all want real democracy so it's worth it."

Those protesters who remained were battling fatigue Monday, as the energy of a once-euphoric campaign began to subside.

"Everyone is just exhausted and we can't go a long, long, long time," said Otto Ng Chun-lung, an 18-year-old sociology student.

Student leaders held a second round of "preparatory talks" with a government representative late Monday, agreeing to move towards formal negotiations.

"We will have multiple rounds of negotiation," said Lester Shum, deputy secretary general of the Hong Kong Federation of Students.

Ray Lau, undersecretary of constitutional and mainland affairs, said: "We hope there will be mutual respect shown during the meeting. We hope we can hold it this week."

Lau will meet the students for a third time on Tuesday to arrange a time and place for talks with the city's number two, Carrie Lam.

Student leaders said the protests would continue as the dialogue with the government progressed, with Joshua Wong -- a 17-year-old firebrand who has become one of the faces of the protest movement -- making a rallying cry in Admiralty for demonstrators to continue occupying the business district.

- Tactical retreat -

The protesters are demanding free and open elections to select the former British colony's next leader in 2017. China's Communist authorities insist only pre-approved candidates will be able to run, a system critics dismiss as "fake democracy".

Handed back to Chinese rule in 1997, Hong Kong is governed under a "one country, two systems" deal that guarantees civil liberties not seen on the mainland, including freedom of speech and the right to protest.

But tensions have been rising over fears that these freedoms are being eroded, as well as rising inequality in the high-cost and space-starved Asian financial hub -- a dynamic that could fuel future unrest.

University leaders and other movement supporters have been trying to persuade the remaining students that they should beat a tactical retreat.

"It's hard to convince the public that continuing the blockade would achieve results," political analyst Willy Lam told AFP.

"If talks between the students and the government prove totally futile... and (Chinese president) Xi Jinping is against concessions, then it's possible to switch on the movement again."