A 13-year-old boy has been shot while walking along a road with his parents in the bank holiday sunshine amid a nationwide spate of violence.

Detectives believe the teenager was struck by a shotgun pellet intended for a target metres away in Harrow, northwest London, where a 15-year-old was shot in the head at around the same time.

The shooting provoked outrage during a tide of bloodshed over the three-day weekend, which saw at least five murders and a major incident unfold in Oxford on Monday.

Police were called to Wealdstone High Street to reports of a shooting at 1.15pm on Sunday, finding the older victim had been shot with several pellets.

Four minutes later, the ambulance service alerted police to a second injured boy nearby.

Police said the 13-year-old had been walking along the road with his parents when he was hit in the head, describing him as an “innocent bystander”.

“It is thought that he was struck by shots fired in the shooting minutes earlier,” a spokesperson for Scotland Yard said.

“He was taken to a west London hospital with non-life threatening injuries and has since been discharged from hospital.”

The older victim remains in hospital but his condition is not thought to be life-threatening.

Police cordon off the scene of the shootings near Wealdstone's High Street (PA)

Police believe a third victim, possibly a friend of the 15-year-old, was shot in the arm during the same incident but left before emergency services arrived.

The manager of a betting shop, who did not give his name, said saw people gathered outside the local Specsavers around a black man on the ground.

“He was holding his head down,” he added. “I could not see his face but could see his white T-shirt was proper covered in blood. He was sitting calmly as the paramedics were looking after him.”

A 39-year-old man has been arrested in connection with the shooting and released under investigation by Trident gang crime command detectives.

Detective Chief Superintendent Simon Rose, Harrow Borough Commander said: “It would appear that the first [15-year-old] victim was approached by two male suspects, one in possession of a shotgun – and shots were fired injuring him and an entirely innocent member of the public.

“This was a callous, reckless and brazen act, without any thought by those responsible for the fact that there were families with children and people in the high street enjoying their weekend. This was quite simply, appalling.

“As a parent myself, I know hearing an incident like this where a child has been shot whilst they have been with their parents will cause alarm. It is senseless and shows an utter disregard for the safety of others.

“I want to assure the communities of Harrow and the wider public we are doing everything we can to catch the suspects responsible. Violent crime has no place on our streets.”

Police have increased patrols in Harrow and across the capital in response to a spike in violence over the bank holiday weekend.

Five people have so far been murdered in Liverpool, London, Macclesfield and Luton, amid a spate of stabbings, shootings and a noxious substance attack.

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Police engaged in a gun battle with an armed man in Oxford city centre on Monday and at least one person was injured in the incident, which is not being treated as terror-related.

Thames Valley Police said officers were called to Paradise Square at 1.15am to reports that a man had access to a gun.

"Shots were fired from the property and police returned fire," a spokesperson said. "Officers are currently negotiating with the man as they work to resolve the situation."

Elsewhere, a teenager was shot in the leg in Clayton, Manchester, in the afternoon.

Police said the young man was with friends when he was attacked at 2.45pm. He was taken to hospital to be treated for serious injuries.

“People will understandably be concerned that someone has been shot in broad daylight on their streets, but I want to assure them we are doing all we can to get to the bottom of what happened," said Detective Inspector Claire Moss.

“On such a warm bank holiday, people will have been in the area and someone out there will have the detail we need to hold the offender to account."

Shortly before 9pm on Sunday, a 37-year-old man was stabbed to death in Macclesfield and died at the scene.

A 15-year-old boy and a 29-year-old man, both from the Macclesfield area, have been arrested as part of ongoing enquiries into the incident in Becks Lane.

On the same night in London, a man was stabbed after questioning a man about his erratic driving.

The 43-year-old man was among residents who approached a suspect driving a blue car in the Perivale district of northwest London about the “nature of his driving in a small residential street”.

“The suspect produced a knife before stabbing the victim and driving away,” a spokesperson for the Metropolitan Police said.

The man remains in a stable condition in hospital following the attack at 9pm on Sunday.

Rhyhiem Ainsworth Barton, 17, was gunned down on a road in Kennington, south London, on 5 May (Reuters)

In a separate incident shortly before 6.30pm, police were flagged down by a member of the public in New Cross, southeast London, after a 22-year-old man was shot.

The injured man was taken by ambulance to hospital where his condition is not life-threatening, Scotland Yard said.

It came shortly after a 20-year-old man was stabbed to death in broad daylight in Luton.

The victim was pronounced dead in Bishopscote Road, which police said was busy at the time.

In the early hours of Sunday morning, three other victims were injured in what police described as a “particularly vicious and unpleasant” noxious substance attack in Hackney.

A fight involving two groups was reported shortly before the incident at 5.20am, which saw a 17-year-old boy and two men aged 22 and 27 taken to hospital.

Police said their injuries, which are not believed to be from acid, could be life-changing.

On the same day, a 20-year-old man was murdered in Liverpool.

He was found with stab wounds in the city centre at 4am and died of his injuries in hospital.

On Saturday morning, a 53-year-old man was shot dead in the Rainhill Stoops area of St Helens.

John Kinsella was attacked on a slip road linking to the M62 at around 7am by a gunman riding a mountain bike, dying at the scene.

No one has yet been arrested over the killings, or a fifth murder in London.

Rhyhiem Ainsworth Barton, a 17-year-old rapper and aspiring architect, was shot dead in the street on Saturday afternoon.

His mother, Pretana Morgan, called for a stop to devastating violence. “Let my son be the last and be an example to everyone,” she added. “Just let it stop.”

Police had announced increased patrols for the the three-day weekend, following months of increased violence that has seen homicides surge by 44 per cent in London in a year.

‘Let my son be the last and be an example to everyone,’ said the mother of Rhyhiem Ainsworth Barton (Handout)

Detective Chief Superintendent Simon Messinger, of the Metropolitan Police, said: ”The violence used has rightly caused concern and we are doing all we can to address this.

“Over the bank holiday weekend, additional officers are on the streets across the capital, working hard to keep London safe.

“They are using highly visible local patrols supported by armed response, traffic motorcycles, dog units, and air support – alongside plain-clothes, intelligence-led operations.”

Scotland Yard is also increasing the use of blanket stop and search powers to seize knives and weapons in designated areas at risk of disorder.

But police have repeatedly said they need help from local communities, councils and the government to stop the root causes of violence and convince teenagers to stop carrying weapons.

The government’s first-ever Serious Violence Strategy spoke of drivers including drug dealing and disputes on social media when it was released last month, but it was heavily criticised for failing to mention plummeting police numbers and cuts to youth services.

Scotland Yard is among the police forces making repeated calls for increased resources amid rising crime, demand and the terror threat, causing council tax contributions for the emergency services to be raised in London.

Sadiq Khan, the mayor, said police were doing “everything they can to bring those responsible to justice and to keep us all safe”.

“However, the police service in London, like the rest of the country, is overstretched and under-resourced,” he added, saying city hall was investing an extra £110m in the Met to maintain police numbers and setting up a £45m youth fund to tackle the causes of violence.

“I refuse to accept that nothing can be done to stem the appalling rise of violent crime we are seeing across the country.”

Statistics released last month showed a 22 per cent annual increase in knife crime recorded by police in England and Wales.