"The search for the unknown perpetrator is ongoing," police wrote on X.
"Possible motives and the exact circumstances of the crime remain unclear."
Cantonal police wrote on X that one person was killed and five injured — some seriously — by a shooting at the event in the canton's capital Aarau, 46 kilometres west of Zurich.
Police spokesperson Pascal Wenzel told Swiss public broadcaster SRF that police were alerted around 2:30am to the shooting.
At the time of the incident, the "Aarau Rave VOL. 7" was taking place at the horse racing track in Aarau's Schachen district, SRF reported.
The fire department cordoned off a large area around the site.
A major police operation was underway and locals were asked to stay away.
Police, firefighters and ambulances were on the scene in large numbers. Even police in Freiburg, in neighboring Germany, took part in search efforts for the suspect, the German news agency dpa reported.
Swiss daily Blick reported that visitors of the rave initially mistook the shots for fireworks until somebody shouted "everyone down."
The newspaper wrote that the shooting took place right after the rave ended. Police later took all remaining visitors to a nearby gym, Blick reported.
Police called on possible witnesses who have video or photos of the incident to share them with police.
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