London fire chief Dany Cotton told BBC radio that it might be "some days yet" before firefighters could say they have reached everyone in the building.
Commander Stuart Cundy said five victims had been formally identified but would not give further details.
Briefing reporters at police headquarters, Cundy became visibly upset as he described conditions in the charred tower, where a search and recovery operation is expected to last weeks.
"The bad reality is, as I've said before, is that due to the intensity of the fire and the devastation within Grenfell Tower that we may not be able to identify everybody that died", he said.
A Book of Condolence for the victims of last week's fire at Grenfell Tower in London is to be opened at Belfast City Hall.
A minute's silence will be held across all government buildings to remember the people who lost their lives and all those affected by the fire last week.
Emergency service workers bowed their heads in respect to the victims of the catastrophic blaze.
The fire has come at a particularly hard time for Prime Minister Theresa May, who was weakened by the loss of her parliamentary majority in a June 8 election and faces arduous talks on Britain's exit from the European Union.
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One of the family's daughters said the community had been "very nice" and the family were getting help.
Jeremy Corbyn, the leader of Britain's main opposition Labour Party, called on the government to take over empty buildings to house the hundreds of residents displaced in the fire.
Grenfell Tower is located in a pocket of social deprivation within the borough of Kensington and Chelsea, one of Britain's wealthiest areas.
Hammond said that will be a focus of the inquiry and investigation.
"We will be looking at all criminal offences that may have been committed by any individual or any organisation", Candy said.
"I believe there may be people who were in Grenfell Tower that people may not know were missing and may not have realised they were in there on the night".
The police chief, who went inside the charred shell of the high-rise tower over the weekend, told reporters: "I've investigated major crime for most of my service and I've seen some awful things but I don't think anything prepared me for what I was going to see when I was in there".
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