The eight-year-old was attacked in a communal area of a block of flats in Bootle at about 5.20pm on Saturday.

Merseyside Police said a 49-year-old woman and 30-year-old man, both from the local area, had been arrested on suspicion of being a person in charge of a dog dangerously out of control and causing injury.

The pair are not related to the injured child.

Officers have also seized the dog involved. The force said the animal was "believed to be an XL bully".

Detective Inspector Gary Stratton said: "This was a horrific attack which has left a young child requiring emergency surgery for injuries to his head.

"I want to reassure people that he is receiving the best possible care and treatment for his injuries, which are described as life-changing."

He added: "This case highlights in the starkest terms the potential dangers of dogs, and I would appeal to anyone with information about dangerous dogs in their area to contact us so that we can take proactive action."

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A police spokesperson said the boy remains in a "serious but stable condition" in hospital following the attack near Bootle's Wadham Road.

They added: "House-to-house enquiries have been carried out in the area and all CCTV opportunities are being explored.

"A number of witnesses have been spoken to at the scene and officers are appealing for further witnesses to come forward and for anyone who may be able to assist enquiries to contact police."

It comes after a ban on XL bully dogs in England and Wales came into force earlier this month.

About 40,000 of the animals have been granted an exemption from the ban.

Owners were allowed to register their pets - in exchange for agreeing to a series of conditions, including having their dogs neutered, microchipped and insured - in order to save them from being put down.

New restrictions on the dogs are also set to be introduced in Scotland.

There are at least 50,000 to 100,000 XL bully dogs in the UK, according to estimates from animal groups.

Earlier this month grandmother Esther Martin, 86, died after being mauled by two dogs in Essex. Police later confirmed the animals were XL bullys.