Police gave organisers last-minute approval for the march on Friday night, after ruling out their proposed route for public safety reasons, reports the South China Morning Post.
The march will now go through the residential neighbourhood of Tai Kok Tsui, adjacent to Mong Kok, rather than deep into the heart of the shopping centre.
The organisers' demands remain the same as at other rallies, that the government look into alleged abuse of police power; completely withdraw the now-suspended extradition bill; exonerate all protesters arrested; implement universal suffrage; and stop calling the protests a riot.
Police have warned that they will have zero tolerance for any violence, because of the march's proximity to the busy Kowloon shopping district.
Saturday's gathering comes after a group of civil servants - ordered to be politically neutral - joined demonstrations on Friday to address protesters' demands, the BBC reported.
Two months of demonstrations sparked by the controversial extradition bill have shown no signs of abating.
Mass protests began in March over the bill which would have allowed extraditions to mainland China.
Although the government has now suspended it, demonstrators want the bill fully withdrawn, and are widening their demands.
Hong Kong, a former British colony, is part of China but enjoys unique freedoms not seen on the mainland.
( With inputs from IANS )