After the first mass rally in the tourist hotspot of Kowloon against the government's now-suspended extradition bill drew an estimated 230,000 peaceful protesters on Sunday afternoon, many remained behind to occupy the streets of Mong Kok and confront police late into the night, reports the South China Morning Post.
Officers warned the protesters that they were taking part in illegal assemblies.
Soon after 3 a.m. on Monday, the police issued a statement saying they had arrested six people in connection with the march and the clash that followed.
Four men and two women, aged between 20 and 66, were taken into custody, the statement added.
One person was arrested during the march for failing to produce proof of identity, while five others were arrested in Mong Kok on suspicion of assaulting a police officer, and the sixth for obstructing officers in the execution of their duties.
In a statement issued ion Monday, a government spokesman slammed the clash on Sunday night.
Their (protesters) actions affected traffic and business activities and also created inconvenience to the public, it said
Hong Kong is a society that upholds the rule of law and its citizens must observe the law, the spokesman added.
Sunday's march was the latest major protest calling for the full withdrawal of the legislation, which would have allowed the transfer of fugitives to mainland China and other jurisdictions with which the city had no extradition agreement, reports the South China Morning Post.
It came after a group of Hong Kong student leaders last week rejected Lam's offer of a private meeting about the recent protests over the now-suspended extradition bill, calling it "too little, too late", the South China Morning Post reported.
The government's offer came after hundreds of mostly young protesters stormed the city's legislature on the night of July 1, writing slogans on the wall, defacing Hong Kong's official emblem and smashing equipment, furniture and work areas.
Among the protesters' demands were for Lam to fully withdraw the bill and to order an independent inquiry into the use of force by police during clashes on June 12.
( With inputs from IANS )