Rupert Carey reports on "a horrendous attack"

Two four-year-old twin girls, a two-year-old boy, their father, their grandmother and their great-grandmother were killed in the blaze at a three-storey building in Chingford.

The seventh victim was a friend of the children's father.

Scotland Yard said the three women were aged 16, 51 and 75. One of the dead men was about 22.

DS James Moore Sutherland: Horrific attack

The police officer in charge of the investigation, Detective Superintendent James Moore Sutherland, said: "We are treating this as a murder. Somebody out there knows who has done this and we need their help.

"This is a horrific attack on innocents. This is the worst I have seen in 31 years in the job."

A plain-clothed police officer has been seen removing a red petrol canister in a sealed bag from the scene.

DS Moore Sutherland: Appealing for information

The seven bodies were left in the burnt-out house until midday on Saturday because it was too dangerous for emergency services to remove them.

Firefighters then used a crane to pass seven stretchers through a second-floor window as they began the harrowing task of retrieving the bodies.

Shortly before 2pm, the dead children's mother arrived at the scene. Weeping and accompanied by two friends, she refused to comment.

A London Fire Brigade spokeswoman said: "The body of an adult male was found in a first-floor rear bedroom.

"Earlier two adult females and three children were found in a second-floor rear bedroom while the body of an adult male was found in the front bedroom on the second floor."

The BBC's Chris Legard: Four generations dead

The alarm was raised shortly before 0100 on Saturday when flames were seen coming from the property.

One adult, believed to be the children's great-grandfather, managed to escape from a first-floor window with the help of neighbours by using a builder's ladder.

The man who survived was taken to Whipps Cross Hospital where he was treated for burns to the hand.

Before daybreak, a bouquet of white flowers had been left on the pavement opposite the burnt-out house.

Neighbours have been shocked by the tragedy

With them was a hand-written note which read: "God bless, Sarah, Lee, Abbie XXX."

Lisa Lewis, a neighbour and good friend of the family, described how she was woken in the early hours by the sounds of screams and cries.

She said: "I could hear the kids coughing and crying. It was terrible ... there was nothing I could do.

"I ran downstairs and called 999 and then went outside. I got ... a window cleaner, to get his ladders off the van. But it was too late. The screaming and crying had stopped. You couldn't see them anymore."

Lisa Lewis: There was screaming, then nothing

Weeping, Miss Lewis, 25, then told how the children's mother arrived at the scene: "I just heard her screaming then 'Get my babies! Get my babies!'

"She collapsed and they took her to hospital," Miss Lewis added.

Another neighbour, Scott Witney, who has lived locally for 22 years and has known the family during that time, said he was shocked at the tragedy.