Police Commissioner Stephen Lo Wai here on Monday condemned the violence that broke out between forces and protestors, which left 28 people injured.
"The mob lost the run of themselves, and their behavior was horrendous," South China Morning Post quoted Lo as saying.
Lo also pledged to track down those responsible for the clashes and hold them accountable.
The forces said 20 men and 17 women were arrested during the clash at Sha Tin's New Town Plaza Shopping mall.
However, lawmakers and district councils accused the force of deploying the wrong tactics by entering the shopping center. They also said that many of the protestors were trying to leave the mall, but police blocked them.
The Hospital Authority has said that at least 28 people suffered injuries after Sunday night's clashes.
Since March, Hong Kong has been shaken by huge demonstrations against the extradition bill or the 'Fugitive Offenders Ordinance', which many fear could be used to deport political activists and dissidents to mainland China.
The bill was proposed on April 3 and its opposers argue that its controversial amendments will leave anyone on Hong Kong soil vulnerable to being grabbed by the Chinese authorities for political reasons or inadvertent business offenses.
Multiple protests sometimes violent continue to take place in the semi-autonomous state despite the city's pro-Beijing leader Carrie Lam publicly apologising for proposing the controversial legislation and announcing later that the bill was "dead".
( With inputs from ANI )