A one-month-old baby is recovering after being dragged from his cot by a fox which tore his finger off.
The animal seriously injured the infant after entering his bedroom in Bromley, south-east London, according to reports.
The attack is the latest in a number of other incidents of foxes attacking humans, prompting calls for a cull on the urban pests.
Surgeons were able to reattach the baby's finger after he was taken to St Thomas's Hospital on Wednesday.
The child's mother was alerted by his screaming and rushed into his room to see his hand lodged "halfway down the animal's throat", the Mail on Sunday said.
A spokesman for the Metropolitan Police, which is investigating the incident, said it would not comment on whether the family had a dog.
London Mayor Boris Johnson said more must be done to tackle the growing problem of urban foxes.
He said: "They may appear cuddly and romantic but foxes are also a pest and a menace, particularly in our cities.
"This must serve as a wake-up call to London's borough leaders, who are responsible for pest control.
"They must come together, study the data, try to understand why this is becoming such a problem and act quickly to sort it out."
Cass Barrett of London Fox Control said residents should stop putting food out for foxes or leaving rubbish around. He said he often heard of the animals coming through people's cat flats after being lured by the scent of pet food.
He said: "Foxes coming into people's houses is nothing new in my experience.
"Foxes are quite accomplished climbers in that a ground floor window I wouldn't imagine should cause too much of a problem for them to get in."
He said his company uses humane methods to exterminate foxes it is called out to get rid of.
But there are also a number of preventative methods to stop them coming into people's gardens such as using special fencing, putting one-way traps on their dens so they can get out but not back in, spraying chemical scents that deter them and even spreading lion dung from zoos.
Mr Barrett added: "I think they're beautiful creatures but unfortunately sometimes they do become a pest.
"In my experience I've never come across any humans that have been actually bitten. But (they've been) intimidated, been worried by foxes, concerned that when they approach them they don't go away."
A next door neighbour of the family, Khadine Peters, 36, said she thought the baby had an older sister and brother.
She told the Daily Mail: "I heard screams, but I didn't think anything of it. Then I saw an ambulance and wondered what was going on.
"They are a nice couple. It's so sad. I hope the baby is okay."
Another neighbour, Paula Wellington, 36, told the paper: "Foxes are menace around here.
"They get very close to you and they are quite intimidating. My daughter is only three and I am worried for her safety."
A police spokesman said: "We were called at 4.38pm on Wednesday February 6 by staff at St Thomas's Hospital to reports a baby boy had been admitted to hospital after being attacked by a fox.
"Police attended to find a four-week-old baby with a hand injury.
"Inquiries continue."
An RSPCA spokeswoman said the only reason a fox would attack a human is due to fear and it is "extremely unusual" for them to hurt children.