The aircraft came down in a field off Bentham Road near Burton in Lonsdale just before midday, police officers said.
Emergency services, including an air ambulance, were called to the scene at the edge of the Yorkshire Dales and police urged people to avoid the area.
The families of those involved were being supported by specially trained officers, police said.
The Air Accidents Investigation Branch (AAIB) confirmed its inspectors were on their way.
In a statement, the AAIB said: "An investigation has been launched and a team of inspectors are travelling to the accident site to begin making inquiries."
Emergency services were called to the scene of the incident off Bentham Road near Burton in Lonsdale at lunchtime today, where a helicopter had crashed into a field.
The incident happened shortly before midday.
People were strongly urged to avoid the area.