A boy was taken to hospital after he was the victim of a suspected XL bully attack in Blackburn, Lancashire.
The dog attack, which was captured on CCTV, took place at about 12.20pm on Cedar Street.
Lancashire Constabulary said a 27-year-old man was arrested and the dog has been seized.
In the video, which was shared on social media, a child and an adult are approaching a junction near a mosque when the dog runs at them and latches on to the boy's coat.
The adult tries frantically to free the boy from the dog's teeth while two other members of the public also attempt to help.
Applications opened for owners to register XL bully dogs ahead of ban (Evening Standard)
XL bully dog: What date does ban on dangerous breed begin? (Yahoo News UK)
One man tries to pry open the dog's mouth to set the boy free while another runs to get extra help.
Police received a report at 12.30pm that a boy had been bitten by a dog and that he was taken to hospital for treatment.
No details have been released about the boy's injuries.
A 27-year-old man from Blackburn was arrested and later released on bail.
A Lancashire Constabulary spokesperson said: "The dog, which at this time we believe is an XL bulldog type, has been seized.
"A short time later it was reported that threats had been made towards the family of the victim.
"A 27-year-old man from Blackburn was arrested on suspicion of assault - ABH [assault occasioning actual bodily harm] and affray and has since been bailed pending further enquiries."
Are XL bully dogs illegal in UK?
Following a spate of high-profile attacks, prime minister Rishi Sunak decided to ban XL bully dogs in England and Wales.
New laws banning the dogs were outlined in parliament at the end of last month.
From 31 December, XL bully type dogs will be added to the list of banned dangerous dogs. This means it will become illegal to breed, sell, advertise, exchange, gift, rehome or abandon XL bully type dogs, or allow them to stray.
For those who already have an XL bully type, from 31 December they will be required to keep the dog on a lead and muzzled when in public.
They must also apply for the government's exemption scheme, which comes into force on 1 February 2024 - from that date it will be illegal to own an XL bully type without a certificate of exemption.
Watch: Rishi Sunak promises to ban XL bully dogs by the end of the year