A 10-year-old boy died when he was attacked by a “bulldog-type” dog at a holiday park, police said.
Police were called to a caravan at Tencreek Holiday Park in Looe, Cornwall, just before 05:00 BST to reports the boy was “unresponsive”.
He died at the scene and a search started to find the dog and owner.
A woman, 28, was arrested on suspicion of manslaughter at 08:00 in Saltash. It is thought the boy had been staying in the same caravan as the dog.
Devon and Cornwall Police said the woman was also arrested on suspicion of having a dog dangerously out of control.
They said the boy’s next of kin were aware and were being supported by police.
Officers said the dog had been found and had been transferred to kennels.
South Western Ambulance Service said paramedics were sent to the park at 04:42.
Police are stopping cars at the entrance to Tencreek Holiday Park, which hosts touring, camping and seasonal pitches as well as static caravans, before allowing them through.
A woman staying at the site with her two children, who asked to remain anonymous, said she woke up earlier to see police and forensic staff “everywhere”.
“It is just really eerie,” she said.
“Loads of people have packed up and left and I have asked to be moved to the furthest part otherwise I was going home.”
The woman said the police presence was frightening for her children.
“It doesn’t feel like a holiday camp – it is horrible,” she added.
In a statement earlier, holiday park manager Robert Ellwood said he had arrived on site this morning to find police already there.
In a further statement, the holiday park management said the child had been attacked by a dog “present in the same caravan”, adding the site would remain open.
It added: “Clearly our thoughts are very much with the family involved – they have our deepest sympathies.”
The mayor of Looe, councillor Armand Toms, said the “tragedy was so sad for the family” and his thoughts were with them.
He said: “This community will do whatever it can to help.
“It always has done and will in the future and I am speaking not as the town’s mayor but as someone born and bred here.”
Mr Toms said the holiday park had been “part of our community” for about 40 years.