Five people, including a nine-week-old baby girl and two other children aged nine and seven, have died in a house fire.
Shabbina Begum, 54, and her 20-year-old daughter Anum Parwaiz Kayani, are also believed to have died in the blaze that broke out in Wake Road, Sharrow, Sheffield.
The cousin of the 54-year-old, Ishfaq Hussain Kayani, said: "It's just a huge tragedy. Words cannot describe how sad this is.
"It's a tragedy beyond description."
He said a nine-week-old baby girl was among those who had died, as well as nine-year-old Adhyan Parwaiz Kayani and seven-year-old Amaan Parwaiz Kayani.
Describing the children as "full of life, quite bubbly and very energetic", he said they had been looking forward to returning to school.
He said of Ms Begum: "She was, to my children, like a mother, like an aunt. The whole community is in huge shock.
"As soon as the news broke just after midnight, we came round. I've been with the family.
"It's so sad. A couple of hours ago the whole family was leading their normal life - quite prosperous, happy.
"Just in a matter of minutes the whole family has been destroyed. The whole family has gone.
"You can well imagine what the children's parents are going through. I don't have the words to describe how the family is feeling, other than shell-shocked, devastated.
"We are a close-knit family, there are enough people around to support the family."
He added: "They were such a lovely family, highly respected. Quite an industrious family who had everything going. This tragedy has struck and we have to try our level best to pull through this."
He described how their mother, Razia Nazim Kayani, survived the blaze but was now in a state of shock and "beyond consoling".
"I believe the mother of the children, I think she was in the house," he said.
"She managed to escape. The grandmother of the children, she made attempts to rescue the children but obviously it wasn't to be.
"She came out then went back in, tried her level best. Frantic attempts were made to rescue the children."
He said the children's father, Nazim Parwaiz Kayani, was out working when the fire broke out.
People living in the area said up to 300 people came out in the street to try to offer help as the emergency services arrived.
Some neighbours reported hearing screams and wailing from the area when they were woken in the early hours.
South Yorkshire Fire and Rescue said the fire began shortly after midnight on the residential street, which is lined with cars on both sides.
A fire brigade spokesman said: "An investigation has commenced, involving police and fire officers, to establish the cause of the fire."
Four fire engines were called to the scene and an aerial ladder was used to tackle the blaze.
Police and ambulance services also went to the house after receiving emergency calls and a cordon was set up in the surrounding streets.
A South Yorkshire Police spokesman said: "At this stage we are not able to confirm where in the house the fire broke out, or if anyone else was injured."
A spokesman for South Yorkshire Fire and Rescue said details about the fire would become clearer later today.
He said: "Our investigators are arriving here at 9am, so we will know more later on this morning."
Phil Shillito, South Yorkshire Fire and Rescue area manager, said 25 firefighters were sent to tackle the blaze.
"This is a tragic reminder of the devastating effects of fire and our thoughts are with the families of those involved in this incident," he said.
"I can confirm that around 25 firefighters and four appliances attended a very challenging incident last night and worked hard to recover and rescue five casualties from the premise. Unfortunately, they didn't survive and we're now working with the police to investigate the cause of fire.
"They were faced with a very challenging fire, lots of flames coming out of the property, and they were aware family members were in the premise and they went in wearing breathing apparatus enabling them to breathe in the hot and smoky environment.
"Unfortunately they did find five casualties in the property."
Local councillor Qubran Hussain, who knew the family, said he believed smoke alarms alerted people in the street who broke windows to try to get into the property.
Mr Hussain said he came down to the scene in the night.
He added: "The lady came out - the grandmother came out. But then she found all the children were inside so she went back in and she's also died."
Mr Hussain said he employed Mrs Begum's husband for many years as a taxi driver in nearby Dronfield. He said he thought the children's father, who is also a taxi driver, was out working at the time.
The whole of Wake Street and parts of neighbouring streets were condoned off today and guarded by a large number of police and community support officers. Used ambulance equipment was strewn on the pavement near the terraced house.