A MURDER probe has been launched after a British man and his family were found dead on a US hiking trail as cops say they have "never seen a case like this".

       Jonathan Gerrish, 45, his wife Ellen Chung, 31, and their one-year-old daughter Muji, were found by search teams on Tuesday in a remote area of the Sierra National Forest in California known as Devil's Gulch.

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       Jonathan Gerrish, 45, his wife Ellen Chung, 31, and their one-year-old daughter Muji Credit: Rosanna Heaslett 6

       Detectives have launched a murder probe over the mysterious deaths Credit: abc7 6

       Cops initially treated the mysterious case as a "hazmat situation" after the family dog was also found dead - but detectives have now opened a murder probe.

       According to the Mirror, Mariposa County Sheriff Jeremy Briese said: "I've been here for 20 years, and I've never seen a death-related case like this.

       "There's no obvious indicators of how it occurred.

       "You have two healthy adults, you have a healthy child and what appears to be a healthy canine all within a general same area.

       "So right now, we're treating the coroner investigation as a homicide until we can establish the cause."

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       The couple had reportedly moved to Mariposa from San Francisco to raise their daughter in "a quiet, slow-paced environment, surrounded by open-air and close to the mountains for hiking and camping adventures".

       Jonathan, who was originally from Lancashire and had worked for Google and Snapchat, was out on Sunday with his family for what was supposed to be a day hike.

       But when their nanny arrived at the family home to look after little Miju, no one answered the door and friends became worried.

       They were reported missing by a relative on Monday and authorities found the family's car near the Sierra National forest gate the same day.

       I think it's going to be a very long and in depth, thorough investigation because it isn't as clear cut as what some cases are.

       Kristie MitchellMariposa County Sheriff's spokeswoman

       Their bodies were located on Tuesday evening two miles from their car in an area with no phone reception.

       Close pal Steve Jaffe described the mysterious deaths as "freaky and strange".

       "You had to figure it wasn't an overnight hike because it's been hot, and they had the baby with them," he told the Mirror.

       "Jon was supposed to work Monday and never showed up. That raised more concerns."

       'DEVASTATED'

       He added: "We're all just devastated.

       "They were really beloved by the people. A super generous, sweet and loving couple that was devoted to their daughter.

       "It's just a tragedy. You have people who pass away and die. And that's always sad.

       "This one is just so freaky and strange, and it's really, really sad. They had so much going for them."

       Following the discovery of the bodies, cops could not initially rule out carbon monoxide emitted from old mines as the cause of death.

       But Sherriff Briese said detectives couldn't find any disused shafts in the area.

       "We have not found any old mine shafts near the area," he said.

       "There are some mine shafts, but we can't confirm if that's the cause yet."

       Autopsies completed on Thursday failed to reveal how the family died, Fox News reports.

       None of the bodies had physical wounds such as gunshots or signs of trauma, and no suicide note was found, Mariposa County Sheriff's spokeswoman Kristie Mitchell said.

       "It makes for a very unique, very strange situation," she said. "I think it's going to be a very long and in depth, thorough investigation because it isn't as clear cut as what some cases are."

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       Jonathan, originally from Lancashire, and his wife Ellen, from Orange, California Credit: Instagram 6

       Jonathan and Ellen had recently moved to the area with their baby daughter Credit: Instagram 6

       Jonathan had previously worked for Google and was working for Snapchat when he died Credit: Facebook