The death toll from the Grenfell Tower fire is believed to be around 80 people, the vast majority of whom were from just 23 flats, police said.
Metropolitan Police Detective Superintendent Fiona McCormack said contact had been made with at least one person from 106 of the 129 flats in the building.
From those flats, 18 people are dead or assumed dead, while the remaining victims were thought to have been in the flats which had not been heard from.
Ms McCormack confirmed more than 60 organisations involved in the tower's refurbishment, which is suspected of aiding the spread of the blaze.
A true total of those killed in the devastating fire may not be known until the end of the year, police believe.
Ms McCormack said a list of tenants provided to police by the Kensington and Chelsea Tenants Management Organisation, which managed the building, was "not accurate".
She said: "We are many months from being able to provide a number which we believe accurately represents the total loss of life inside Grenfell Tower.
"Only after we have completed a search and recovery operation, which will take until the end of the year.
"What I can say is that we believe that around 80 people are either dead or sadly missing and I must presume that they are dead."
Efforts to establish who was missing in the wake of the fire were focused on talking to friends, families and neighbours of those in Grenfell Tower, Ms McCormack said.
She said: "On the first day of our work we were provided with a list by the tenant management organisation of who they had recorded living at Grenfell Tower.
"We quickly identified by the end of the first day that this list was not accurate."
She added: "What we know is that it would be impossible for anyone to produce a list to show exactly who was at Grenfell Tower that night, that includes the people who were living there or who were visiting."
The 23 flats which were said to have no survivors were spread between the 11th floor and the 23rd.
A handful of flats were still too unstable for police to carry out further investigation, the officer said.
She added: "There are 23 flats that despite huge investigative efforts, we have been unable to trace anyone that lives there.
"At this stage, we must presume, that no-one in those flats survived, that includes anyone who lived there or was visiting them."
Police have examined "every imaginable source" of information about who was in the building, "from government agencies to fast food companies", she added.
A couple who were missing and assumed dead had actually been on holiday at the time of the blaze, according to the detective.
A criminal investigation is taking place to establish if charges will be brought against those involved in renovating the building, including manslaughter.
"We are continuing to seize material on a daily basis and the number of companies and organisations that we know so far had played a role in the refurbishment is over 60," Ms McCormack said.
Survivors of the fire were also said to have given statements.
The detective said: "We are working very hard to identity everyone who died in the fire, but the tragic reality is that due to the intense heat of the fire, there are some people we may never identify.
"Tragically, we are preparing families and loved ones for the fact we many never recover the remains of their loved ones."
A renewed call was made to groups with lists of suspected victims and those who were living in the building illegally to come forward.
Ms McCormack said: "Our aim is the same - we want to understand the true human cost of this tragedy."
Pressed on whether the death toll could climb to triple figures, Ms McCormack said: "I've said I believe it could increase, I don't think it's going to be triple, no.
"What I will only work on is facts, these are families we are dealing with, they are numbers to people, but they are not to me, they are victims to me and that is really essential."
It is expected that the number of companies found to have worked on the Grenfell Tower refurbishment is likely to rise, she said.
She added: "So far everybody has been compliant and we've actually been provided with a wealth of documents already."