A man has been arrested on suspicion of murder after a woman who was about eight months pregnant was stabbed to death on Saturday.

Paramedics delivered the 26-year-old woman’s baby as she was dying, after they found her at a residential address in Croydon, south London.

The child was taken to hospital and the Metropolitan police said it remained in a “critical condition”.

A 37-year-old man was arrested and is being held in custody while officers from of the Met’s Homicide and Serious Crime Command launched an investigation.

DCI Mick Norman, who is leading the inquiries, said: “This is a horrific incident in which a young mother has lost her life and her child is critically ill. Our sympathies go out to her devastated family; they are being supported by specially trained officers following this awful event, and I would ask that they are left alone at this time as they come to terms with the enormity of what has happened.

“A large crime scene is in place, and is likely to be in place for some time. Residents should be aware that if they have any concerns, or information they would like to share with us, that they can speak to any of the officers there, or call our incident room.

“At the forefront of our inquiries is understanding what exactly has led to these tragic circumstances, and we are doing everything we can to establish the facts.”

London mayor Sadiq Khan reacted to the murder on Twitter, saying: “Violence against women is endemic in society and devastating murders in the home, like this one, show the scale of the problem we face.

“My prayers are with this innocent child, and with the mother it has so tragically lost.”

Police and the London ambulance service were called at 3.30am on Saturday to an address in Raymead Avenue in Thornton Heath, a residential street lined with houses and flats, after reports that a woman was having a cardiac arrest.

Officers and paramedics arrived to discover the woman was suffering from stab injuries.

Quick Guide Knife crime in the UK Show What is the scale of the problem? Police chiefs have described the recent spate of knife crime as ‘a national emergency’. In the first two months of 2019 there were 17 homicides in London alone, where 35% of all knife crimes are committed. The number of NHS England admissions among people aged 10-19 with knife wounds has risen 60% in five years, surpassing 1,000 last year. The number of knife and offensive weapon offences in England and Wales have risen to their highest level for nearly a decade, with the number of cases dealt with by the criminal justice system up by more than a third since 2015. Knife crime-related offences recorded by the police rose by 8% in England and Wales in 2018. Figures on sentences handed out for such crimes, published by the Ministry of Justice, showed there were 22,041 knife and weapon offences formally dealt with by the criminal justice system in the year ending March 2019. This is the highest rate since 2010, when the number was 23,667.

What happens to people caught with knives? In the year ending March 2019, 37% of knife and offensive weapon offences resulted in an immediate custodial sentence, compared with 22% in 2009, when the data was first published. The average length of the custodial sentences rose to the longest in a decade, from 5.5 months to 8.1 months. Are younger people more at risk of being involved in knife crime? The MoJ figures revealed that the number of juvenile offenders convicted or cautioned for possession or threats using a knife or offensive weapon increased by almost half (48%) between the year ending March 2015 and the year ending March 2019. The increase in adult offenders over the same period was smaller, at 31%. However, adult offenders still accounted for 74% of the total increase in cautions and convictions received for those offences in that period. What are the government doing about knife crime? In March 2019 chancellor, Philip Hammond, handed an extra £100m to police forces in England and Wales after a spate of fatal stabbings led to a renewed focus on rising knife crime and police resources. In the same month more than 10,000 knives were seized and 1,372 suspects arrested during a week-long national knife crime crackdown. Officers carried out 3,771 weapons searches, during which 342 knives were found. Another 10,215 were handed in as part of amnesties.

A new Offensive Weapons Act was passed in May 2019, making it illegal to possess dangerous weapons including knuckledusters, zombie knives and death star knives. It also made it a criminal offence to dispatch bladed products sold online without verifying the buyer is over 18.

A London ambulance service spokesman said: “We sent an incident response officer, two ambulance crews, two medics in response cars and an advanced paramedic to the scene. We also dispatched London’s Air Ambulance.

“We took one person to hospital as a priority. Sadly, despite the extensive efforts of medics, another person died at the scene.”

The Met said officers were “keeping an open mind” as to what might have motivated the attack. The woman’s next of kin have been informed although she has yet to be formally identified. Police said a postmortem examination will take place in due course.

Neighbours said that three woman, one of whom was pregnant, lived at the house and they had a small dog.

One said that she had got up at about 3.30am to perform her prayers when she heard a dog barking at the house, which is two doors down.