“The search for the perpetrators, whose identities are currently unknown, is under way,” they said on X, adding that the motives and exact circumstances were not yet known.
Police launched what they called a “large-scale response” to find the perpetrators after the incident in Aarau, north of Zurich.
An AFP journalist saw armed officers deployed on the highway up to 30 kilometres (18 miles) from the site of the shooting.
Swiss newspaper Blick reported on its website that the shots were fired before 3:00 am (0100 GMT) on the sidelines of the Aarauer Rave.
Some 3,500 people attended the annual techno party between 3:00 pm on Saturday and 2:00 am on Sunday.
Police spokeswoman Vanessa Rumpold was quoted as telling the newspaper that the shooting happened at the racecourse where the event was held.
“Several shots were fired within a large group of people,” she added.
Witnesses told Blick that shots were fired at about 2:30 am while the rave was still going on and that many people took refuge in a nearby gymnasium. Partygoers at first thought the shots were fireworks.
One told the newspaper there was a “burst of gunfire”.
A local resident in Aarau posted a video on social media showing deserted streets and what sounded like several gunshots in the background.
Media reports said an army helicopter was deployed in the cantonal capital, Aargau, as well as numerous police officers, rescue workers and medical teams.
