Questions are being asked about whether escape routes and fire prevention measures were "adequate" at a block of flats where fire left six people dead, Harriet Harman said.
Three young children were among those killed in the fire at 12-storey Lakanal Flats, in Camberwell, south London, last night.
Ms Harman, the area's MP, said people were "asking questions" about fire escape routes at the flats.
She added: "There will have to be a thorough investigation in to what caused this fire and whether the prevention was adequate.
"There are many blocks with one central stairwell and questions will have to be asked about what happens when a fire breaks out."
Several residents said the complicated layout of the flats made the evacuation difficult while onlookers described seeing those trapped inside screaming for help.
A six-year-old child, a woman in her thirties and another adult, died inside the building, emergency services said.
A three-week-old baby, a seven-year-old and an adult woman were pronounced dead in hospital after last night's blaze.
Chief Supt Wayne Chance said the fire started inside a fourth floor flat and is being treated as suspicious.
Thirty people were rescued from the block in Sceaux Gardens, off Dalwood Street, and 15 people were taken to hospital yesterday, including three who died.
Eleven people had been released and one man, a firefighter, remains in hospital but his condition is not thought to be serious, Mr Chance added.
The bodies of three of those killed remain inside the block which is being treated as a crime scene until the cause of the fire is determined, he said.
The victims came from a "number of families" and were still being identified.
Mr Chance said officers were dealing with a "large and complex scene" and added: "The investigation is likely to take some time."
Southwark Council Leader Nick Stanton said it was likely to be "days if not weeks" before residents could return to their homes after the "ghastly" incident.
Miss Harman, who is Leader of the House of Commons, met families who escaped the blaze and emergency service workers today and said she was "struck by how calm and immensely brave people were".
London Fire Brigade said the blaze began on the fourth floor yesterday afternoon and "spread rapidly" to the 11th floor.
Carol Cooper, 38, who lives on the seventh floor, described "seeing people and children waving for help".
"Everyone was here. But it took too long for them to get in there and do something. It just seemed like it took too long.
"I think that's because it's just like a maze in there."
She said that the tenants had called for the block to be demolished three years ago but had been told it was a listed building, one of the earliest council houses in south-east London and could not be knocked down. Instead, the council fitted new windows and electrical cabling.
One woman, who did not want to be named, described the tower block as a "death trap" which should have been torn down years ago.
Ed Hammond, 37, an accountant who lives on the seventh floor, agreed that the flats were "death traps".
"If the fire is in the central area, you would virtually have nowhere to go," he said.
"I hate it," he said. "It's the safety, it's just not right."
Zahera Chaudry, 21, whose sister was in a first-floor flat when the blaze broke out, said: "These buildings should have been torn down years ago."
She said there was no central fire alarm system in operation but some of the individual flats were fitted with alarms.
Her sister, Jasmine, said said her first warning of the fire was when smoke came into her living room yesterday afternoon and she was forced to flee with her three children.
"I have always said that these buildings should have come down.
"Now look what's happened.
"You can see how quickly the fire spread."
Charles Douglas, 56, was in his top floor flat when the blaze broke out and said he waited on his balcony until the escape route was clear as everyone was rushing down the stairs.
He said the layout of the flats made it difficult for everyone to get out quickly.
He said there were 96 flats in the block and added: "A lot of people were panicking but I tried to stay calm and think clearly."
London Fire Brigade said about 30 people who had been in "immediate peril" were evacuated from the building.
Neighbours described seeing people screaming for help as the fire took hold.
Lincent Johnson, 28, who lives across the street said: "The people were in the windows, screaming out for help.
"There was panic, there were a lot of people screaming.
"It wasn't that big at first but it started to spread so quickly."
Abenet Tsejage, of nearby Havil Street also saw people screaming for help and said she saw one mother dangle a baby from a window as if she was about to drop her child.
But she said the woman did not let go and she believed they were rescued.
Ms Tsejage, who has lived in the area for 15 years, said: "Quite a few people were in shock and very upset. It makes you really frightened.
"As a community you would like to give all those who live there a home but you just don't know how to help."
Police believe they know the identities of the six dead and are waiting to inform next-of-kin and for formal identification before they release their names.
Post mortem examinations are being arranged.
A single bunch of flowers was placed in a children's play area inside the police cordon behind the tower block.
Several people who lived near have spoken of it being a stable community where many people have lived for a number of years.
Neighbours said there was a friendly atmosphere, with relatively little trouble.
One message read: "For such a tragic loss."
Unharmed survivors were taken to an emergency centre in a nearby church hall set up by Southwark Council and the British Red Cross last night, while the injured were taken to three London hospitals.
About 150 people were without accommodation last night. The vast majority stayed with friends or family and 20 were provided with accommodation by the council.
Miss Harman said she had been keeping Number 10 informed of the "very tragic situation".
Mr Stanton praised the work of the emergency services, saying he was "in awe of the courage and professionalism" shown.
Today a heavy smell of soot and smoke hung in the air as the building was made safe so fire investigators could get inside.
The rear of the building was blackened, with several parts of the wall missing, and the area immediately around the building remained sealed off.
Mr Chance said: "We would always treat a situation like this as suspicious because we don't know the cause of the fire.
"So we are treating the scene as a crime scene on the basis that we don't know how this fire started."
Paul Glenny, a firefighter who battled the blaze, said: "I've been in the job for 30 years, and I've never seen anything like it.
"The hot weather and the fact that people's windows were open made the fire what it was."
Ian Wingfield, a local Labour councillor and the spokesperson for public housing in the borough, said he believed it was the "worst tower block disaster in history".
He called for a full public investigation into such housing across the country.
He said: "We're living in the 21st century and people are still living in housing like this.
"Unless we get that investigated, people lives are under threat."
Talking about the blaze, he said: "It's very disturbing. All the events around this fire are extremely tragic.
"This is an horrendous incident.
"My heart goes out to the families of all those who've lost loved ones.
"We need to ensure justice is given for these needless deaths and insure that nothing like this happens again."
Police today named five of the six victims.
They were: Helen Udoaka, 34, and her three-week-old daughter Michelle; Dayana Francisquini, 26 and Filipe Francisquini, 3, and Catherine Hickman, 31.Reuse content