Swiss police said on Sunday that one person was dead and five others injured after shots were fired overnight at an event in Aarau in northern Switzerland.
It is unclear who fired the shots. Some of the injured were seriously wounded, police said.
A major police operation is under way at the site, and the public was urged to avoid the area.
"The search for the unknown perpetrator is ongoing. Possible motives and the exact circumstances of the offence remain unclear," the police wrote on X.
A video published by the Swiss newspaper Blick, which is said to have been recorded near the scene of the crime, features around 10 shots.
The newspaper quoted a police spokeswoman as saying the scene of the crime was a horse racing track. A rave was taking place there at the time of the shots at about 3 am (0100 GMT).
Those attending the event were taken to a nearby gymnasium by police.
Aarau, in the Swiss canton of Aargau, is situated about 40 kilometres west of Zurich.
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