A 31-year-old woman has been arrested after a dog left a four year-old boy with serious injuries.

The youngster was attacked by the bull mastiff-type animal after going to visit a friend’s house in Wellesboune Place, Norris Green, Merseyside Police said in a statement.

A neighbour who fought the dog off “probably” saved his life, the force added.

However, the boy still sustained serious injuries and was taken to hospital where he is receiving treatment.

His condition was described as “serious but stable”.

The dog has been seized and a woman, from Norris Green, has been arrested on suspicion of having a dangerously out of control dog.

She will be interviewed by detectives.

In a statement, Detective Inspector Chris Hawitt said dog owners need to muzzle their pets in public spaces if they could be aggressive.

“This incident has left a young child with serious injuries to his face and head and will have been an extremely distressing incident for all who witnessed it,” he said.

“I would like to commend the neighbour whose quick thinking and selfless swift actions have probably saved the life of this young boy, who has suffered life-changing injuries.

“Our enquiries into the full circumstances of the incident are ongoing and we have seized the dog for the safety of the community and to establish its breed.”

He said officers are “keen” to speak to witnesses.

“We have a dedicated sergeant who reviews all cases concerning dangerous dogs and are keen to speak to any witnesses who may have seen the incident or this dog on previous occasions,” he said.

“I want to emphasise that dog owners need to be mindful of their dogs’ behaviour at all times, particularly where young children may be around the dog. And if owners take their dogs into public spaces, they should keep their pet on a lead and muzzled if it is liable to be aggressive.”

Anyone with information is asked to contact the social media desk at @MerPolCC, call 101 citing reference number 929 of August 13, or call the independent charity @CrimestoppersUK anonymously on 0800 555 111.