Two of those on board have been named locally as Kevin and Ruth Burke from Hulcote, near Milton Keynes.
They were believed to have been travelling to Dublin, where Mrs Burke was born, for a christening with three other adult family members.
A massive air and land search was launched on Wednesday when the aircraft vanished after leaving the Luton area.
Kevin and Ruth Burke are believed to have been directors of the Milton Keynes-based Staske Construction company - the registered owner of a Twin Squirrel helicopter.
This was the model that vanished from radar contact while over Caernarfon Bay.
It is believed Mr Burke was originally from Manchester and was a qualified pilot.
Supt Gareth Evans, of North Wales Police, said the crash site was in the Rhinog mountains between Harlech and Trawsfynydd and the bodies of all five people on board had been found.
A mountain rescue team found the wreckage.
The Air Accident Investigation Branch are now leading an investigation of the forensic recovery of the aircraft once specialist officers start recovery of the bodies.
But the police have said they might have to suspend recovery for the night due to worsening weather conditions and "treacherous terrain".
Police said they were not aware of any plan for the helicopter to stop in Caernarfon as part of its route.
Formal identification of the bodies has not yet taken place and the coroner for north west Wales, Dewi Pritchard-Jones, has opened an investigation.
Police have not revealed the exact location of the crash and have asked for members of the public to stay away from the site "to allow emergency services and personnel access". An air exclusion zone is also in place.
"Their recovery is not just important to their families but also the investigation as it may help identify any contributory factors," added Supt Evans.
Family of those killed have been informed and the police have confirmed all five adults are "part of the same extended family from the Milton Keynes area".
Initial searches on Wednesday followed the intended flight plan of the aircraft over the Irish Sea.
But the Coastguard said on Thursday that inquiries led them to divert their efforts to Snowdonia National Park.
Prior to the crash site being discovered, UK Coastguard duty commander Mark Rodaway said: "These aircraft normally carry beacons that we can track by satellite - they're activated by salt water - we've not seen any of that and also mobile phone data has aided our inquiries in shifting inland."
Welsh Secretary Alun Cairns said the UK government would offer its full support to the investigation.
The Department of Foreign Affairs in Dublin said it "stood by to offer consular assistance".
The Eurocopter AS55 Ecureuil 2 (Twin Squirrel), made by Airbus, has a cruising speed of 140mph (225km/h) and a range of nearly 440 miles (700km).
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Five members of the same family have been killed in a helicopter crash in north Wales.