The hard landing occurred for “unknown reasons” at 2.30pm near a helicopter base at Erstfeld, Uri cantonal police said.
The aircraft was carrying four employees of Rega, the Swiss company that provides emergency medical assistance by air.
The three seriously injured victims were taken to hospital, police said
According to the 20 Minuten newspaper, the helicopter landed 20 metres from the base, one of 13 Rega bases around Switzerland.
A witness told the newspaper the landing gear of the aircraft appeared to be damaged.
Reports said the helicopter was returning from a rescue mission when it crashed on landing.
Rega said the cause of the accident was initially not known.
The Swiss Accident Investigation Board (SUST) has opened an investigation into the incident.