Gunfire erupted shortly before 10:30 p.m. in the Green Hill community near Kingstown, according to Acting Commissioner of Police Trevor Bailey, who addressed the killings during a Saturday news conference.
Officers responding to the scene found two bodies on a public road, while a woman was found dead inside a vehicle parked nearby, Bailey said.
Four additional people were taken to Milton Cato Memorial Hospital with gunshot injuries. Two were treated and released, while two remained hospitalized at the time of the police briefing.
Assistant Commissioner of Police Brenton Smith said investigators were working to identify whoever was responsible and cautioned against speculation while the investigation remained active.
Police were also investigating a separate shooting in Ottley Hall early Saturday and had not determined whether the two incidents were connected.
"That determination must be made by investigators based on the evidence and not on rumors or assumptions," Smith said.
The killings come as authorities grapple with gun and gang violence across the small island nation. Smith said 37 murders have been recorded in St. Vincent and the Grenadines so far this year.
Bailey acknowledged that police have seen instances of retaliatory violence involving rival groups but did not link the Green Hill killings to gang activity. Asked whether criminal groups could be connected to the latest violence, police said the investigation had not reached a point where they could make such a determination.
Local outlet iWitness News reported that the Green Hill attack was one of several shootings in recent years in which multiple people were killed, including a July shooting in Kingstown that left three people dead.
The outlet reported the identities of Friday's four victims based on its own sources, though police had not officially released their names when the report was published.
Police appealed for anyone with photographs, video, surveillance footage or information about people or vehicles potentially connected to the shootings to contact investigators.