Experts from the 9/11 terror attack have been brought in to help provide specialist knowledge to the police investigation into the Grenfell Tower fire.
Metropolitan Police Deputy Commissioner Craig Mackey said the "extraordinary size" of the potential crime scene meant those who worked in the aftermath of the Twin Towers disaster in 2001 were being called upon.
Mr Mackey said the 200 UK officers already working on the case were faced with sifting through 15 tonnes of debris on each of the building's 24 floors.
It came as Scotland Yard confirmed the latest victim as 68-year-old Majorie Vital. At least 80 people are thought to have died in the devastating fire in north Kensington on June 14.
Giving an update at the London Assembly Police and Crime Committee, Mr Mackey said: "This is one of the most complex recovery operations we've seen.
"The people we're taking advice from - which gives you an idea of the complexity - are some of the people who worked on 9/11 and the fall of the Towers.
"It is an extraordinary size of crime scene."
Mr Mackey said it was necessary to call on US counterparts because of their experience in a "comparable" operation.
He said: "Without wanting to be too graphic - but I hope it helps explain - the fire in some parts of that building (Grenfell) burned at over 1,000 degrees for a considerable period of time.
"So we are now working through floor by floor and it is literally a case of sifting and working through the debris - sadly, the remains - to try and desperately identify parts of people so we can reunite (the remains with families).
"There's about 15 tonnes of material to work through and we think we'll be working through until Christmas time in terms of working through that scene gathering all the evidence.
"We're working with everyone you'd expect to see.
"The role of disaster victim identification is actually something UK policing has built up a level of knowledge in over a number of years. The only comparable advice we can find is from the challenge that was 9/11."
He said the investigation was "going to be one of the largest and most complex" in the Met's history, but added that he would be "guessing" if he had to put a timeframe on when any arrests might be made.
Mr Mackey's comments came as Downing Street responded to the official appointment of the new leader of Kensington and Chelsea Council at a stormy meeting on Wednesday.
Newly-elected Elizabeth Campbell faced boos and heckling at a packed public meeting in Kensington Town Hall, but said she was stepping up to the challenge and pledged to rebuild trust among the community "brick by brick" amid calls for her to resign.
Ms Campbell replaced Nicholas Paget-Brown, who stepped down on June 30 amid fierce criticism of the council's response to the Grenfell tragedy.
The first full council meeting since the fire five weeks ago saw a public gallery filled with former Grenfell Tower residents and an over-spill room containing at least 150 community members and volunteers.
Outside, a group of demonstrators holding Justice for Grenfell placards were gathered.
The Prime Minister's official spokesman said: "We have said that the appointment of a new leader offers an important opportunity for fresh leadership.
"It is important that the council works hard to regain the trust of the local community."
Latest figures from the Department for Communities and Local Government showed that cladding from 263 high-rise residential buildings in 57 local authority areas failed combustibility tests.
These include a combined school and residential building, while additional samples from seven buildings at six NHS Trusts and another school also failed.