The victim, a resident of the Lake Geneva region, died around 2pm after being found in the hallway of a building on the Rue de la Bryonne, police said.
Emergency officials attempted to treat the man but he died from wounds inflicted by a knife.
The local prosecutor immediately launched a criminal investigation into the apparent attack.
Police were unable to say where the man was attacked.
“This person was found wounded in the hallway of a building,” cantonal police spokesman Jean.Christophe Sauterel told the ATS news agency.
“(The person) died shortly after, despite the intervention of emergency services.”
The force issued a call for anyone with information about the assault to contact investigators by phoning 021 644 44 44 or contacting the nearest police station.
Police described the victim as about 180 centimetres tall with medium long tousled hair and a goatee.
He was wearing dark jeans, dark t-shirt, dark grey vest and black Adidas running shoes with a fluorescent pink logo.
Residents in the normally quiet town on Lake Geneva, known for housing the headquarters of giant food company Nestlé, appeared stunned by the apparent killing, 20 Minutes newspaper reported.
A woman who works for a business on a street near where the victim was found recalled seeing a man walking bent double and clutching his stomach at around 1.15pm, the newspaper said.
The woman said she saw the man go into a passage that leads to street where the victim was later found.