Hundreds of thousands of protesters rallied without incident in torrential rain on Sunday in the eleventh week of what have been often violent demonstrations.

"I sincerely hope that this was the beginning of society returning to peace and staying away from violence," Lam said.

"We will immediately start the work to establish a platform for dialogue. This dialogue, I hope, will be based on a mutual understanding and respect and will find a way out for today's Hong Kong."

Anger erupted in June over a now-suspended bill that would allow criminal suspects in the former British colony to be extradited to mainland China.

But the unrest broadened to worries about the erosion of freedoms guaranteed under the "one country, two systems" formula put in place after Hong Kong's return to China in 1997.

Further protests are planned in the next few days, including one by MTR subway workers on Wednesday, secondary school students on Thursday and accountants on Friday.

The chaos has spread overseas. Twitter Inc and Facebook Inc said on Monday they had dismantled a social media campaign originating in mainland China that sought to undermine protests in Hong Kong.

Police have been criticised for using increasingly aggressive tactics to break up demonstrations but there was a minimal police presence on Sunday and no arrests were made. More than 700 people have been arrested since June.

The protests have hit the economy of Hong Kong, one of the world's busiest ports, with the Asian financial hub on the verge of its first recession in a decade.

Lam said Hong Kong had "unique advantages in attracting overseas companies", stressing the rule of law, but warned of the risk of pressure on the economy which shrank 0.4 per cent in April-June from the previous quarter.

"The Hong Kong economy is facing the risk of downturn. We can see this from the data in the first half. Actually, I think the data in the first half has not fully reflected the seriousness of the problem," she said.

Australian Associated Press