Protest organisers said about two million people choked Hong Kong's streets on Sunday - despite Lam's decision to indefinitely suspend passage of the bill a day earlier.
Critics fear the Beijing-backed law will entangle people in China's notoriously opaque and politicised courts and damage the city's reputation as a safe business hub.
Although Lam offered a rare concession on Saturday, she stopped short of committing to permanently scrapping the unpopular law.
Her gesture was swiftly rejected by protest leaders who called on her to resign, shelve the bill entirely and apologise for police using tear gas and rubber bullets earlier in the week.
But Lam - the first woman to get the international financial hub's top job - continues to enjoy support from the Chinese leadership.
"The central government will continue to firmly support the chief executive and efforts by the government of the Special Administrative Region to govern according to law," Chinese foreign ministry spokesman Lu Kang told a regular briefing.
Lam took over as Hong Kong's chief executive in March 2017 when a committee stacked with Beijing loyalists voted her into office.
Beijing had earlier backed Lam's decision to suspend the bill saying it was an attempt to "listen more widely" to different views and "restore calm."
But Lu from China's foreign ministry said the protests are "not in line with the mainstream public opinion in Hong Kong."
"Many facts have shown that foreign governments and even some politicians have been making inflammatory remarks since the decision of the Hong Kong government to start amending the extradition ordinance in February," Lu said.