One person has died and five people are injured after shots were fired at an event in northern Switzerland overnight, local police say.
"The manhunt for the unknown perpetrator is under way," Aargau Cantonal Police said in a statement. "Possible motives as well as the exact circumstances of the crime are still unclear."
The force told Swiss media that the shooting took place near a horse racing track in Schachen, Aarau, some 46km (29 miles) west of Zurich.
A rave was scheduled to take place in the area into the early hours of Sunday.
An area around the racing track, the town's swimming pool and sports field has been cordoned off, with the public urged to stay away.
A large contingent of officers has also been deployed beyond Aarau "as a precaution", police said.
The force asked witnesses to submit photographs and video from the scene.
Images from Aarau early on Sunday showed a heavy police presence in the area, with an armoured vehicle seen blocking a road.
In addition to police and fire officials, the regional disaster response unit (KKE) was deployed, according to broadcaster SRF.
It also reported that a Swiss Army helicopter could be seen surveying the area in the early hours.
