A boy has died after being bitten by a dog.
The incident happened at a property in a residential street in Halstead, Essex, at 5.40pm on Thursday.
A 29-year-old woman has been arrested for allowing a dog to be dangerously out of control and injuring a person, Essex Police said.
The dog has been seized by police and placed in kennels.
The East of England Ambulance Service said an air ambulance was called to the scene, while it also sent two rapid response vehicles, paramedics and an ambulance to the property.
A spokesman said: "At the scene, a young child was treated for life-threatening injuries before being airlifted to Addenbrooke's Hospital (in Cambridge).
"Sadly, despite the best efforts of everyone involved, the child has died. Our thoughts are with the family involved at this time."
It comes just days after a 52-year-old man was attacked and killed by a dog which had been returned to its owner despite concerns that it was dangerous.
David Ellam was out walking with his Yorkshire terrier close to his home in Huddersfield on Monday when he was attacked by another dog. He later died in hospital.
West Yorkshire Police said the animal had been seized by police following a visit by a dog warden in June, but had been returned to its owner on August 8 after it was determined that it was not a banned breed.
The Independent Police Complaints Commission (IPCC) has said it will launch an investigation into Monday's attack.
Dogs are responsible for thousands of attacks on humans every year - but only a few dangerous breeds have been legally outlawed.
Figures last year showed that dog attacks have soared 76% in the past decade, with more than 7,000 people taken to hospital between 2014 and 2015.
The Dangerous Dogs Act was brought in 25 years ago to force police and animal rescue organisations to euthanise certain types of dog considered a threat to people.
But the scope of the Act means that even if there are concerns that a specific dog is dangerous, unless it is a banned breed the action local authorities can take is more limited.