Fire service advice to "stay put" in the Grenfell Tower fire had "effectively failed" within around half an hour of the fire starting, a report for the blaze inquiry has found.
A safety expert said there was "an early need for total evacuation", but it was not an "easy decision to make".
Dr Barbara Lane also suggested cladding was the primary cause of the spread of June's fire, which caused 72 deaths.
Safety measures were "inadequate" and the events "catastrophic", she said.
Dr Lane's report was one of five published from experts at the start of the fact-finding stage of the public inquiry.
The hearing was played the audio of the first 999 call made on the night, by the tenant of flat 16 - where the fire started - Behailu Kebede, who survived.