Police cordoned off Tiki and Matipo streets and an officer on the scene confirmed it was "probably" related to the shooting.
There were more than 10 police vehicles in attendance, and five or six people were in handcuffs, being spoken to by officers. A number of them were wearing the colours of the Black Power gang, known to have a strong presence in the Gonville-Castlecliff area of the city.
Detective Inspector Ross McKay said a number of people were in police custody in Whanganui last night as part of the investigation into the Ratana shooting.
The armed offenders squad and the Eagle helicopter assisted in the execution of multiple search warrants.
"Those in custody as a result of the warrants are helping police with inquiries," McKay said.
"Some are expected to be released on bail, and some held in custody, as potential charges are confirmed."
He said police had also recovered a number of firearms, firearms parts, and ammunition in yesterday's raids.
The Whanganui community could expect to see an increased number of armed police, investigative staff, and the Eagle helicopter in the area.
Inspector Mark Harrison said there would likely be more search warrants carried out.
Police staff throughout the lower North Island had witnessed a surge of gang numbers travelling to Whanganui over the weekend to attend Ratana's tangi, and Harrison said that had led to police bolstering their numbers.
"We're expecting an influx of gang members into town," Harrison said.
"We just want to reassure the people of Whanganui that we will be increasing our visibility around the town, so don't worry too much."
Harrison said there were probably more than 100 gang members in the city, compared to the usual two or three dozen people "that you would loosely associate with gangs".
He said the Eagle helicopter would allow police to assess any incidents in a very short amount of time because of the small size of the city.