A 20-year-old man has been charged with 26 offences following an investigation into a series of alleged incidents in Sydney's west over the past month.

Police began investigating in August after receiving reports of a man allegedly performing sexual acts in front of multiple women in the Parramatta area.

Investigators allege several of the incidents occurred at a shopping centre on Church Street, Parramatta, between August 23 and September 12. Police also allege that a similar incident occurred in Haymarket on September 7.

Following inquiries into the reports, officers executed a search warrant at a property on Lyton Street, Blacktown, at about 11:30am on September 17.

Police allege that small quantities of ketamine and cannabis were located during the search. Clothing and other items that investigators considered relevant to the investigation were also allegedly seized.

Later that day, a 20-year-old man attended Parramatta Police Station, where he was arrested and subsequently charged.

The charges include 12 counts of carrying out a sexual act with another person without consent. He also faces five counts of stalking or intimidation with intent to cause fear of physical or other harm.

Three further charges relate to allegedly behaving offensively in or near a public place or school. Police also charged the man with two counts of allegedly harassing retail workers without causing actual bodily harm and one count of allegedly intimidating a retail worker.

Another charge alleges that he assaulted a police officer while the officer was carrying out their duties, although no actual bodily harm was alleged in that charge.

The remaining two charges relate to alleged possession of prohibited drugs.

Police refused bail and the man was scheduled to appear before Parramatta Local Court on Friday, September 18.

The investigation began after reports from members of the public and involved inquiries into incidents allegedly occurring at different locations in Sydney.

The charges remain allegations. The accused is entitled to the presumption of innocence unless and until proven guilty in court.

Police have continued their investigation into the circumstances surrounding the alleged incidents and have encouraged anyone with relevant information to assist investigators.

The case will now proceed through the NSW court system, where the allegations and evidence will be considered.