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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Two leading groups, Jaysh al-Islam and Ahrar al-Sham, which formed a pact last year, both say the plane was shot down.
Syrian state media said the crash was caused by a technical fault.
Jaysh al-Islam, the larger of the two groups, posted footage online which it claimed showed the pilot being held after ejecting from the jet.
The video, bearing Jaysh al-Islam's logo, showed an object engulfed in flames followed by an interview with the supposed pilot.
The man gave his name as Nawras Hassan, as well as his date of birth and hometown. He said he was based in Dumair air base and that he had been a pilot for 16 years.
A later image posted by the group appeared to show the pilot dead.
Jaysh al-Islam said in a statement that the pilot was captured by the Joint Operations Room - the name adopted by a collection of rebel groups in the region including Jaysh al-Islam, Ahrar al-Sham, and Jabhat al-Nusra.
Jaysh al-Islam said the pilot was captured by militants from the al-Qaeda-linked Jabhat al-Nusra, who were supposed to hand him over but killed him instead.
Neither the claims nor the footage have been independently verified.
More than 280,000 have been killed and millions displaced by Syria's five-year conflict, according to UN estimates.
Five members of the same family have been killed in a helicopter crash in north Wales.
[NEXT_CONCEPT]
Syrian rebels say they shot down a Syrian air force jet and blamed an al-Qaeda-linked group for killing the pilot.